anchor
stringlengths 50
3.92k
| positive
stringlengths 55
6.16k
|
|---|---|
Studying neutral hydrogen structures during the epoch of reionization
using fractal dimensions: Fractal dimensions can be used to characterize the clustering and
lacunarities in density distributions. We use generalized fractal dimensions to
study the neutral hydrogen distribution (HI) during the epoch of reionization.
Using a semi-numeric model of ionized bubbles to generate the HI field, we
calculate the fractal dimensions for length scales $\sim 10 h^{-1}$ cMpc. We
find that the HI field displays significant multifractal behaviour and is not
consistent with homogeneity at these scales when the mass averaged neutral
fraction $\bar{x}_{\rm HI}^M \gtrsim 0.5$. This multifractal nature is driven
entirely by the shapes and distribution of the ionized regions. The sensitivity
of the fractal dimension to the neutral fraction implies that it can be used
for constraining reionization history. We find that the fractal dimension is
relatively less sensitive to the value of the minimum mass of ionizing haloes
when it is in the range $\sim 10^9 - 10^{10} h^{-1} M_{\odot}$. Interestingly,
the fractal dimension is very different when the reionization proceeds
inside-out compared to when it is outside-in. Thus the multifractal nature of
HI density field at high redshifts can be used to study the nature of
reionization. | Bound on the graviton mass from Chandra X-ray cluster sample: We present new limits on the graviton mass using a sample of 12 relaxed
galaxy clusters, for which temperature and gas density profiles were derived by
Vikhlinin et al (astro-ph/0507092) using Chandra X-ray observations. These
limits can be converted to a bound on the graviton mass, assuming a non-zero
graviton mass would lead to a Yukawa potential at these scales. For this
purpose, we first calculate the total dynamical mass from the hydrostatic
equilibrium equation in Yukawa gravity and then compare it with the
corresponding mass in Newtonian gravity. We calculate a 90 % c.l. lower/upper
limit on the graviton Compton wavelength/ mass for each of the 12 clusters in
the sample. The best limit is obtained for Abell 2390, corresponding to
$\lambda_g > 3.58\times 10^{19}$ km or $m_g<3.46 \times 10^{-29}$ eV. This is
the first proof of principles demonstration of setting a limit on the graviton
mass using a sample of related galaxy clusters with X-ray measurements and can
be easily applied to upcoming X-ray surveys such as eRosita. |
How to calculate dark matter direct detection exclusion limits that are
consistent with gamma rays from annihilation in the Milky Way halo: When comparing constraints on the Weakly Interacting Massive Particle (WIMP)
properties from direct and indirect detection experiments it is crucial that
the assumptions made about the dark matter (DM) distribution are realistic and
consistent. For instance, if the Fermi-LAT Galactic centre GeV gamma-ray excess
was due to WIMP annihilation, its morphology would be incompatible with the
Standard Halo Model that is usually used to interpret data from direct
detection experiments. In this article, we calculate exclusion limits from
direct detection experiments using self-consistent velocity distributions,
derived from mass models of the Milky Way where the DM halo has a generalized
NFW profile. We use two different methods to make the mass model compatible
with a DM interpretation of the Galactic centre gamma-ray excess. Firstly, we
fix the inner slope of the DM density profile to the value that best fits the
morphology of the excess. Secondly, we allow the inner slope to vary and
include the morphology of the excess in the data sets used to constrain the
gravitational potential of the Milky Way. The resulting direct detection limits
differ significantly from those derived using the Standard Halo Model, in
particular for light WIMPs, due to the differences in both the local DM density
and velocity distribution. | Lyman alpha Radiative Transfer with Dust: Escape Fractions from
Simulated High-Redshift Galaxies: The Lyman alpha emission line is an essential diagnostic tool for probing
galaxy formation and evolution. Not only is it commonly the strongest
observable line from high-redshift galaxies but from its shape detailed
information about its host galaxy can be revealed. However, due to the
scattering nature of Lya photons increasing their path length in a non-trivial
way, if dust is present in the galaxy the line may be severely suppressed and
its shape altered. In order to interpret observations correctly, it is thus of
crucial significance to know how much of the emitted light actually escapes the
galaxy.
In the present work, using a combination of high-resolution cosmological
hydro-simulations and an adaptively refinable Monte Carlo Lya radiative
transfer code including an advanced model of dust, the escape fractions f_esc
of Lya radiation from high-redshift (z = 3.6) galaxies are calculated. In
addition to the average escape fraction, the variation of f_esc in different
directions and from different parts of the galaxies is investigated, as well as
the effect on the emergent spectrum.
Escape fractions from a sample of simulated galaxies of representative
physical properties are found to decrease for increasing galaxy virial mass
M_vir, from f_esc approaching unity for M_vir ~ 10^9 M_sun to f_esc less than
10% for M_vir ~ 10^12 M_sun. In spite of the dust being almost grey, it is
found that the emergent spectrum is affected non-uniformly, with the escape
fraction of photons close to the line center being much higher than of those in
the wings, thus effectively narrowing the Lya line. |
The Milky Way rotation curve in Horava - Lifshitz theory: The Horava - Lifshitz (HL) theory has recently attracted a lot of interest as
a viable solution to some quantum gravity related problems and the presence of
an effective cosmological constant able to drive the cosmic speed up. We show
here that, in the weak field limit, the HL proposal leads to a modification of
the gravitational potential because of two additive terms (scaling respectively
as $r^2$ and $r^{-4}$) to the Newtonian $1/r$ potential. We then derive a
general expression to compute the rotation curve of an extended system under
the assumption that the mass density only depends on the cylindrical
coordinates $(R, z)$ showing that the HL modification induces a dependence of
the circular velocity on the mass function which is a new feature of the
theory. As a first exploratory analysis, we then try fitting the Milky Way
rotation curve using its visible components only in order to see whether the HL
modified potential can be an alternative to the dark matter framework. This
turns out not to be the case so that we argue that dark matter is still needed,
but the amount of dark matter and the dark halo density profile have to be
revised according to the new HL potential. | The Non-Linear Fisher Information content of cosmic shear surveys: We quantify the Fisher information content of the cosmic shear survey
two-point function as a function of noise and resolution. The two point
information of dark matter saturates at the trans-linear scale. We investigate
the impact of non-linear non-Gaussianity on the information content for
lensing, which probes the same dark matter. To do so we heavily utilize N-body
simulations in order to probe accurately the non-linear regime. While we find
that even in a perfect survey, there is no clear saturation scale, we observe
that non-linear growth induced non-Gaussianity could lead to a factor of ~4
reduction for the common Dark Energy figure of merit. This effect is however
mitigated by realistic levels of shot noise and we find that for future
surveys, the effect is closer to a factor of 1.5. To do so, we develop a new
scheme to compute the relevant covariant matrix. It leads us to claim an
unbiased estimator with an order of magnitude improvement in accuracy with only
twice more simulations than previously used. Finally, we evaluate the error on
the errors using bootstrap methods. |
Standardizing reverberation-measured C IV time-lag quasars, and using
them with standardized Mg II quasars to constrain cosmological parameters: We use 38 C IV quasar (QSO) reverberation-mapped (RM) observations, which
span eight orders of magnitude in luminosity and the redshift range $0.001064
\leq z \leq 3.368$, to simultaneously constrain cosmological-model and QSO
radius-luminosity ($R-L$) relation parameters in six cosmological models, using
an improved technique that more correctly accounts for the asymmetric errors
bars of the time-lag measurements. We find that $R-L$ relation parameters are
independent of the cosmological models used in the analysis and so the $R-L$
relation can be used to standardize the C IV QSOs. The C IV QSO cosmological
constraints are consistent with those from Mg II QSOs, allowing us to derive
joint C IV + Mg II QSO cosmological constraints which are consistent with
currently accelerated cosmological expansion, as well as consistent with
cosmological constraints derived using better-established baryon acoustic
oscillation (BAO) and Hubble parameter [$H(z)$] measurements. When jointly
analyzed with $H(z)$ + BAO data, current C IV + Mg II QSO data mildly tighten
current $H(z)$ + BAO data cosmological constraints. | Chameleon Field Theories: Chameleons are light scalar fields with remarkable properties. Through the
interplay of self-interactions and coupling to matter, chameleon particles have
a mass that depends on the ambient matter density. The manifestation of the
fifth force mediated by chameleons therefore depends sensitively on their
environment, which makes for a rich phenomenology. In this article, we review
two recent results on chameleon phenomenology. The first result a pair of no-go
theorems limiting the cosmological impact of chameleons and their
generalizations: i) the range of the chameleon force at cosmological density
today can be at most ~Mpc; ii) the conformal factor relating Einstein- and
Jordan-frame scale factors is essentially constant over the last Hubble time.
These theorems imply that chameleons have negligible effect on the linear
growth of structure, and cannot account for the observed cosmic acceleration
except as some form of dark energy. The second result pertains to the quantum
stability of chameleon theories. We show how requiring that quantum corrections
be small, so as to allow reliable predictions of fifth forces, leads to an
upper bound of m < 0.0073 (\rho/ 10 g cm^{-3})^{1/3} eV for gravitational
strength coupling, whereas fifth force experiments place a lower bound of
m>0.0042 eV. An improvement of less than a factor of two in the range of fifth
force experiments could test all classical chameleon field theories whose
quantum corrections are well-controlled and couple to matter with nearly
gravitational strength regardless of the specific form of the chameleon
potential. |
Discriminating Topology in Galaxy Distributions using Network Analysis: (abridged) The large-scale distribution of galaxies is generally analyzed
using the two-point correlation function. However, this statistic does not
capture the topology of the distribution, and it is necessary to resort to
higher order correlations to break degeneracies. We demonstrate that an
alternate approach using network analysis can discriminate between
topologically different distributions that have similar two-point correlations.
We investigate two galaxy point distributions, one produced by a cosmological
simulation and the other by a L\'evy walk. For the cosmological simulation, we
adopt the redshift $z = 0.58$ slice from Illustris (Vogelsberger et al. 2014A)
and select galaxies with stellar masses greater than $10^8$$M_\odot$. The two
point correlation function of these simulated galaxies follows a single
power-law, $\xi(r) \sim r^{-1.5}$. Then, we generate L\'evy walks matching the
correlation function and abundance with the simulated galaxies. We find that,
while the two simulated galaxy point distributions have the same abundance and
two point correlation function, their spatial distributions are very different;
most prominently, \emph{filamentary structures}, absent in L\'evy fractals. To
quantify these missing topologies, we adopt network analysis tools and measure
diameter, giant component, and transitivity from networks built by a
conventional friends-of-friends recipe with various linking lengths. Unlike the
abundance and two point correlation function, these network quantities reveal a
clear separation between the two simulated distributions; therefore, the galaxy
distribution simulated by Illustris is not a L\'evy fractal quantitatively. We
find that the described network quantities offer an efficient tool for
discriminating topologies and for comparing observed and theoretical
distributions. | 3D Reconstruction of the Density Field: An SVD Approach to Weak Lensing
Tomography: We present a new method for constructing three-dimensional mass maps from
gravitational lensing shear data. We solve the lensing inversion problem using
truncation of singular values (within the context of generalized least squares
estimation) without a priori assumptions about the statistical nature of the
signal. This singular value framework allows a quantitative comparison between
different filtering methods: we evaluate our method beside the previously
explored Wiener filter approaches. Our method yields near-optimal angular
resolution of the lensing reconstruction and allows cluster sized halos to be
de-blended robustly. It allows for mass reconstructions which are 2-3
orders-of-magnitude faster than the Wiener filter approach; in particular, we
estimate that an all-sky reconstruction with arcminute resolution could be
performed on a time-scale of hours. We find however that linear, non-parametric
reconstructions have a fundamental limitation in the resolution achieved in the
redshift direction. |
The Two-Phase, Two-Velocity Ionized Absorber in the Seyfert 1 Galaxy NGC
5548: We present an analysis of X-ray high quality grating spectra of the Seyfert 1
galaxy NGC 5548 using archival Chandra HETGS and LETGS observations for a total
exposure time of 800ks. The continuum emission is well represented by a
powerlaw plus a black-body component. We find that the well known X-ray warm
absorber in this source consists of two different outflow velocity systems.
Recognizing the presence of these kinematically distinct components allows each
system to be fitted independently, each with two absorption components with
different ionization levels. The high velocity system consists of a component
with temperature of 2.7X10^6K and another component with temperature of
5.8X10^5K. The low-velocity system required also two absorbing components, one
with temperature of 5.8X10^5K; the other with lower temperature (3.5X10^4K).
Once these components are considered, the data do not require any further
absorbers. In particular, a model consisting of a continuous radial range of
ionization structures is not required. The two absorbing components in each
velocity system are in pressure equilibrium with each other. This suggests that
each velocity system consists of a multi-phase medium. This is the first time
that different outflow velocity systems have been modelled independently in the
X-ray band for this source. The kinematic components and column densities found
from the X-rays are in agreement with the main kinematic components found in
the UV absorber. This supports the idea that the UV and X-ray absorbing gas is
part of the same phenomenon. NGC 5548 can now be seen to fit in a pattern
established for other warm absorbers: 2 or 3 discrete phases in pressure
equilibrium. There are no remaining cases of a well studied warm absorber in
which a model consisting of a multi-phase medium is not viable. | The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic
Survey DR16 luminous red galaxy and emission line galaxy samples: cosmic
distance and structure growth measurements using multiple tracers in
configuration space: We perform a multi-tracer analysis using the complete Sloan Digital Sky
Survey IV (SDSS-IV) extended Baryon Oscillation Spectroscopic Survey (eBOSS)
DR16 luminous red galaxy (LRG) and the DR16 emission line galaxy (ELG) samples
in the configuration space, and successfully detect a cross correlation between
the two samples, and find the growth rate to be $f\sigma_8=0.342 \pm 0.085$
($\sim25$ per cent accuracy) from the cross sample alone. We perform a joint
measurement of the baryonic acoustic oscillation (BAO) and redshift space
distortion (RSD) parameters at a single effective redshift of $z_{\rm eff}=
0.77$, using the auto- and cross-correlation functions of the LRG and ELG
samples, and find that the comoving angular diameter distance $D_M(z_{\rm
eff})/r_d = 18.85\pm 0.38$, the Hubble distance $D_H(z_{\rm eff})/r_d = 19.64
\pm 0.57$, and $f\sigma_8(z_{\rm eff}) = 0.432 \pm 0.038$, which is consistent
with a $\Lambda$CDM model at $68\%$ CL. Compared to the single-tracer analysis
on the LRG sample, the Figure of Merit (FoM) of $\alpha_{\perp}, \alpha_{||}$
and $f\sigma_8$ is improved by a factor of $1.11$ in our multi-tracer analysis,
and in particular, the statistical uncertainty of $f\sigma_8$ is reduced by
$11.6 \%$. |
Improved model-independent constraints on the recombination era and
development of a direct projection method: The precision of recent experiments such as ${\it Planck}$ have allowed us to
constrain standard and non-standard physics (e.g., due to dark matter
annihilation or varying fundamental constants) during the recombination epoch.
However, we can also probe this era of cosmic history using model-independent
variations of the free electron fraction, $X_{\rm e}$, which in turn affects
the temperature and polarization anisotropies of the cosmic microwave
background. In this paper, we improve on the previous efforts to construct and
constrain these generalised perturbations in the ionization history, deriving
new optimized eigenmodes based on the full Planck 2015 likelihood data,
introducing the new module 'FEARec++'. We develop a direct likelihood sampling
method for attaining the numerical derivatives of the standard and non-standard
parameters, and discuss complications arising from the stability of the
likelihood code. We improve the amplitude constraints of the ${\it Planck}$
2015 principal components constructed here, $\mu_1=-0.09\pm0.12$,
$\mu_2=-0.17\pm0.20$ and $\mu_3=-0.30\pm0.35$, finding no indication for
departures from the standard recombination scenario. The third mode error is
reduced by $60\%$. We utilise an efficient eigen-analyser that keeps the
cross-correlations of the first three eigenmodes to $\xi_{\mu,\mu'}<0.1\%$
after marginalisation for all the considered data combinations. We also propose
a new projection method for estimating constraints on the parameters of
non-standard recombination. Using our eigenmodes, this allows us to recreate
the ${\it Planck}$ constraint on the two-photon decay rate, $A_{\rm
2s1s}=7.60\pm0.64$, giving an estimate to within $\simeq 0.05\sigma$ of the
full MCMC result. The improvements on the analysis using the ${\it Planck}$
data will allow us to implement this new method for analysis with fundamental
constant variations in the future. | Galactic winds and stellar populations in Lyman $α$ emitting
galaxies at z ~ 3.1: We present a sample of 33 spectroscopically confirmed z ~ 3.1
Ly$\alpha$-emitting galaxies (LAEs) in the Cosmological Evolution Survey
(COSMOS) field. This paper details the narrow-band survey we conducted to
detect the LAE sample, the optical spectroscopy we performed to confirm the
nature of these LAEs, and a new near-infrared spectroscopic detection of the [O
III] 5007 \AA\ line in one of these LAEs. This detection is in addition to two
[O III] detections in two z ~ 3.1 LAEs we have reported on previously (McLinden
et al 2011). The bulk of the paper then presents detailed constraints on the
physical characteristics of the entire LAE sample from spectral energy
distribution (SED) fitting. These characteristics include mass, age,
star-formation history, dust content, and metallicity. We also detail an
approach to account for nebular emission lines in the SED fitting process -
wherein our models predict the strength of the [O III] line in an LAE spectrum.
We are able to study the success of this prediction because we can compare the
model predictions to our actual near-infrared observations both in galaxies
that have [O III] detections and those that yielded non-detections. We find a
median stellar mass of 6.9 $\times$ 10$^8$ M$_{\odot}$ and a median star
formation rate weighted stellar population age of 4.5 $\times$ 10$^6$ yr. In
addition to SED fitting, we quantify the velocity offset between the [O III]
and Ly$\alpha$ lines in the galaxy with the new [O III] detection, finding that
the Ly$\alpha$ line is shifted 52 km s$^{-1}$ redwards of the [O III] line,
which defines the systemic velocity of the galaxy. |
Constraining dark energy fluctuations with supernova correlations: We investigate constraints on dark energy fluctuations using type Ia
supernovae. If dark energy is not in the form of a cosmological constant, that
is if the equation of state is not equal to -1, we expect not only temporal,
but also spatial variations in the energy density. Such fluctuations would
cause local variations in the universal expansion rate and directional
dependences in the redshift-distance relation. We present a scheme for relating
a power spectrum of dark energy fluctuations to an angular covariance function
of standard candle magnitude fluctuations. The predictions for a
phenomenological model of dark energy fluctuations are compared to
observational data in the form of the measured angular covariance of Hubble
diagram magnitude residuals for type Ia supernovae in the Union2 compilation.
The observational result is consistent with zero dark energy fluctuations.
However, due to the limitations in statistics, current data still allow for
quite general dark energy fluctuations as long as they are in the linear
regime. | Time delay between images of the lensed quasar UM673: We study brightness variations in the double lensed quasar UM673 (Q0142-100)
with the aim of measuring the time delay between its two images. In the paper
we combine our previously published observational data of UM673 obtained during
the 2003 - 2005 seasons at the Maidanak Observatory with archival and recently
observed Maidanak and CTIO UM673 data. We analyze the V, R and I-band light
curves of the A and B images of UM673, which cover ten observational seasons
from August 2001 to November 2010. We also analyze the time evolution of the
difference in magnitudes between images A and B of UM673 over more than ten
years. We find that the quasar exhibits both short-term (with amplitude of \sim
0.1 mag in the R band) and high-amplitude (\sim 0.3 mag) long-term variability
on timescales of about several months and several years, respectively. These
brightness variations are used to constrain the time delay between the images
of UM673. From cross-correlation analysis of the A and B quasar light curves
and error analysis we measure the mean time delay and its error of 89 \pm11
days. Given the input time delay of 88 days, the most probable value of the
delay that can be recovered from light curves with the same statistical
properties as the observed R-band light curves of UM673 is 95{+5/-16}{+14/-29}
days (68 and 95 % confidence intervals). Analysis of the V - I color variations
and V, R and I-band magnitude differences of the quasar images does not show
clear evidence of the microlensing variations between 1998 and 2010. |
Shock Waves and Cosmic Ray Acceleration in the Outskirts of Galaxy
Clusters: The outskirts of galaxy clusters are continuously disturbed by mergers and
gas infall along filaments, which in turn induce turbulent flow motions and
shock waves. We examine the properties of shocks that form within $r_{200}$ in
sample galaxy clusters from structure formation simulations. While most of
these shocks are weak and inefficient accelerators of cosmic rays (CRs), there
are a number of strong, energetic shocks which can produce large amounts of CR
protons via diffusive shock acceleration. We show that the energetic shocks
reside mostly in the outskirts and a substantial fraction of them are induced
by infall of the warm-hot intergalactic medium from filaments. As a result, the
radial profile of the CR pressure in the intracluster medium is expected to be
broad, dropping off more slowly than that of the gas pressure, and might be
even temporarily inverted, peaking in the outskirts. The volume-integrated
momentum spectrum of CR protons inside $r_{200}$ has the power-law slope of
$4.25 - 4.5$, indicating that the average Mach number of the shocks of main CR
production is in the range of $\left< M_s \right>_{\rm CR} \approx 3 - 4$. We
suggest that some radio relics with relatively flat radio spectrum could be
explained by primary electrons accelerated by energetic infall shocks with $M_s
>~ 3$ induced in the cluster outskirts. | Constraints on Primordial non-Gaussianity from Future HI Intensity
Mapping Experiments: The primordial non-Gaussianity induces scale-dependent bias of the \hi with
respect to the underlying dark matter, which exhibits features on the very
large scales of the 21-cm power spectrum potentially observable with \hi
intensity mapping observations. We forecast the prospective constraints on the
four fundamental shapes of primordial non-Gaussianity (local, equilateral,
orthogonal, and enfolded), with the current and future \hi intensity mapping
experiments, BINGO, FAST, and SKA-I. With the current configuration of the
experiments and assumed one-year observation time, we find that the SKA-I will
provide tighter constraints on the local shape of primoridal non-Gaussianity
than Planck. The results are $(\sigma_{f^{\rm local}_{\rm NL}},\sigma_{f^{\rm
equil}_{\rm NL}},\sigma_{f^{\rm orth}_{\rm NL}},\sigma_{f^{\rm enfold}_{\rm
NL}})_{\rm SKA-I}=(0.54, 86, 25, 43)$, $(\sigma_{f^{\rm local}_{\rm
NL}},\sigma_{f^{\rm equil}_{\rm NL}},\sigma_{f^{\rm orth}_{\rm
NL}},\sigma_{f^{\rm enfold}_{\rm NL}})_{\rm BINGO}=(17, 100, 128, 164)$,
$(\sigma_{f^{\rm local}_{\rm NL}},\sigma_{f^{\rm equil}_{\rm
NL}},\sigma_{f^{\rm orth}_{\rm NL}},\sigma_{f^{\rm enfold}_{\rm NL}})_{\rm
FAST}=(9.5, 44, 75, 94)$. If the lower frequency band of FAST can be used, the
constraint on local-type primordial non-Gaussianity will be
$\sigma_{f_\mathrm{NL}}\sim1.62$ which is better than Planck. In addition, if
the observation time for FAST could be extended to two years, the constraint on
the equilateral shape of primordial non-Gaussianity would be improved to
$\sigma_{f_\mathrm{NL}}\sim32$. Similarly, if the observational time of SKA-I
could be extended to two years, the constraint on local and orthogonal shapes
could be improved to $0.43$ and $20$, respectively, achieving better
constraints than Planck. |
Gamma-Ray Burst Afterglows as Analogues of High Frequency-Peaked BL Lac
Objects: The spectral properties from radio to optical bands are compared between the
18 optically bright Gamma-ray burst afterglows and well established
power-spectrum sequence in Blazars. The comparison shows that the afterglows
are well agreement with the well known Blazar sequence (i.e., the $\nu
L_{\nu}(\mathrm{5GHz})$-$\alpha_{\mathrm{RO}}$ correlation, where
$\alpha_{\mathrm{RO}}$ is the broad-band spectral slope from radio to optical
bands). The afterglows are, however, clustered at the low luminosity end of the
sequence, which is typically occupied by high frequency-peaked BL Lac objects.
The correlation suggests that Gamma-ray burst afterglows share the similar
emission process with high frequency-peaked BL Lac objects. We further identify
a deviation at a significance level larger than 2$\sigma$ from the sequence for
three typical optically "dark" bursts. The deviation favors a heavy extinction
in optical bands for the "dark" bursts. The extinction $A_V$ is estimated to be
larger than 0.5-0.6 magnitude from the $\nu
L_{\nu}(\mathrm{5GHz})$-$\alpha_{\mathrm{RO}}$ sequence. | Obscured star-formation and environment in the COSMOS field: We investigate the effects of the environment on star-formation in a sample
of massive luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs)
with S(24 micron)>80 uJy and i+<24 in the COSMOS field. We exploit the accurate
photometric redshifts in COSMOS to characterize the galaxy environment and
study the evolution of the fraction of LIRGs and ULIRGs in different
environments in the redshift range z=0.3-1.2 and in bins of stellar mass. We
find that the environment plays a role in the star formation processes and
evolution of LIRGs and ULIRGs. We find an overall increase of the ULIRG+LIRG
fraction in an optically-selected sample with increasing redshift, as expected
from the evolution of the star formation rate density. We find that the
ULIRG+LIRG fraction decreases with increasing density up to z~1, and that the
dependence on density flattens with increasing redshift. We do not observe the
reversal of the star-formation rate density relation up to z=1 in massive LIRGs
and ULIRGs, suggesting that such reversal might occur at higher redshift in
this infrared luminosity range. |
The X-ray invisible Universe. A look into the halos undetected by
eROSITA: The paper presents the analysis of optically selected GAMA groups and
clusters in the SRG/eROSITA X-ray map of eFEDS (eROSITA Final Equatorial Depth
Survey), in the halo mass range $10^{13}-5{\times}10^{14}$ $M_{\odot}$ and at
$z < 0.2$. All X-ray detections have a clear GAMA counterpart, but most of the
GAMA groups in the halo mass range $10^{13}-10^{14}$ $M_{\odot}$ remain
undetected. We compare the X-ray surface brightness profiles of the eROSITA
detected groups with the mean stacked profile of the undetected low-mass halos
at fixed halo mass. Overall, we find that the undetected groups exhibit less
concentrated X-ray surface brightness, dark matter, and galaxy distributions
with respect to the X-ray detected halos. The mean gas mass fraction profiles
are consistent in the two samples within 1.5$\sigma$, indicating that the gas
follows the dark matter profile. The low mass concentration and the magnitude
gap indicate that these systems are young. They reside with a higher
probability in filaments while X-ray detected groups favor the nodes of the
Cosmic Web. Because of the lower central emission, the undetected systems tend
to be X-ray under-luminous at fixed halo mass and to lie below the
$L_X-M_{halo}$ relation. Interestingly, the X-ray detected systems inhabiting
the nodes scatter the less around the relation, while those in filaments tend
to lie below it. We do not observe any strong relationship between the system
X-ray appearance and the AGN activity. We cannot exclude the role of the past
AGN feedback in affecting the gas distribution over the halo lifetime. However,
the data suggests that the observed differences might be related to the halo
assembly bias. | Nonhelical turbulence and the inverse transfer of energy: A parameter
study: We explore the phenomenon of the recently discovered inverse transfer of
energy from small to large scales in decaying magnetohydrodynamical turbulence
by Brandenburg et al. (2015) even for nonhelical magnetic fields. For this
investigation we mainly employ the Pencil-Code performing a parameter study,
where we vary the Prandtl number, the kinematic viscosity and the initial
spectrum. We find that in order to get a decay which exhibits this inverse
transfer, large Reynolds numbers ($\mathcal{O}\sim 10^{3}$) are needed and low
Prandtl numbers of the order unity $Pr = 1$ are preferred. Compared to helical
MHD turbulence, though, the inverse transfer is much less efficient in
transferring magnetic energy to larger scales than the well-known effect of the
inverse cascade. Hence, applying the inverse transfer to the magnetic field
evolution in the Early Universe, we question whether the nonhelical inverse
transfer is effective enough to explain the observed void magnetic fields if a
magneto- genesis scenario during the electroweak phase transition is assumed. |
Deep learning dark matter map reconstructions from DES SV weak lensing
data: We present the first reconstruction of dark matter maps from weak lensing
observational data using deep learning. We train a convolution neural network
(CNN) with a Unet based architecture on over $3.6\times10^5$ simulated data
realizations with non-Gaussian shape noise and with cosmological parameters
varying over a broad prior distribution. We interpret our newly created DES SV
map as an approximation of the posterior mean $P(\kappa | \gamma)$ of the
convergence given observed shear. Our DeepMass method is substantially more
accurate than existing mass-mapping methods. With a validation set of 8000
simulated DES SV data realizations, compared to Wiener filtering with a fixed
power spectrum, the DeepMass method improved the mean-square-error (MSE) by 11
per cent. With N-body simulated MICE mock data, we show that Wiener filtering
with the optimal known power spectrum still gives a worse MSE than our
generalized method with no input cosmological parameters; we show that the
improvement is driven by the non-linear structures in the convergence. With
higher galaxy density in future weak lensing data unveiling more non-linear
scales, it is likely that deep learning will be a leading approach for mass
mapping with Euclid and LSST. | Hubble Diagram Dispersion From Large-Scale Structure: We consider the effects of large structures in the Universe on the Hubble
diagram. This problem is treated non-linearly by considering a Swiss Cheese
model of the Universe in which under-dense voids are represented as negatively
curved regions of space-time. Exact expressions for luminosity distances and
redshifts are used to investigate the non-linear effects of structure on the
magnitudes of astrophysical sources. It is found that the intervening voids we
consider, between the observer and source, produce changes in apparent
magnitude of less than 0.012. Sources inside voids, however, can be affected
considerably at redshifts below z~0.5. By averaging observable quantities over
many randomly generated distributions of voids we find that the presence of
these structures has the effect of introducing a dispersion around the mean,
which itself can be displaced the background value. Observers in an
inhomogeneous universe, who take averages of observables along many different
lines of sight, may then introduce systematic biases, and under-estimate
errors, if these effects are not taken into account. Estimates of the potential
size of these effects are made using data from simulated large-scale structure. |
Constraints on the Nambu-Goto cosmic string contribution to the CMB
power spectrum in light of new temperature and polarisation data: Cosmic strings generate vector and tensor modes in the B-channel of
polarization, as well as the usual temperature power spectrum and E-mode
polarization spectrum. We use the power spectrum obtained from high-resolution
Nambu-Goto cosmic string simulations together with the Planck and BICEP2
likelihoods to explore the degeneracies appearing between cosmic strings and
other cosmological parameters in different inflationary scenarios, as well as
the constraints that can be imposed on cosmic strings in each of these
situations. In standard $\Lambda$CDM, the Planck likelihood yields an upper
limit $G\mu<1.49 \times 10^{-7}$ (95% confidence). We also analyse the
possibility of explaining the BB power spectrum signal recently detected by the
BICEP2 probe. We find that cosmic strings alone are able to explain only part
of the B-mode polarization signal. Apart from the standard $\Lambda$CDM model,
we look at the following non-minimal parameters: the running of the spectral
index, non-zero tensor-to-scalar ratio, additional degrees of freedom
($N_{eff}$) and sterile neutrinos. We find that in both Planck and BICEP2
scenarios adding $N_{eff}$ induces degeneracies between cosmic strings and
$N_{eff}$ and other $\Lambda$CDM parameters. With $N_{eff}$ a larger
contribution from cosmic strings is allowed, even favoured, but after combining
with large-scale structure data, such as BAOs, strings remain strongly
constrained. | The (not so) squeezed limit of the primordial 3-point function: We prove that, in a generic single-field model, the consistency relation for
the 3-point function in the squeezed limit receives corrections that vanish
quadratically in the ratio of the momenta, i.e. as (k_L/k_S)^2. This implies
that a detection of a bispectrum signal going as 1/k_L^2 in the squeezed limit,
that is suppressed only by one power of k_L compared with the local shape,
would rule out all single-field models. The absence of this kind of terms in
the bispectrum holds also for multifield models, but only if all the fields
have a mass much smaller than H. The detection of any scale dependence of the
bias, for scales much larger than the size of the haloes, would disprove all
single-field models. We comment on the regime of squeezing that can be probed
by realistic surveys. |
The Thermal Sunyaev-Zel'dovich Effect from Massive, Quiescent 0.5 $\leq$
z $\leq$ 1.5 Galaxies: We use combined South Pole Telescope (SPT)+Planck temperature maps to analyze
the circumgalactic medium (CGM) encompassing 138,235 massive, quiescent 0.5
$\leq$ z $\leq$ 1.5 galaxies selected from data from the Dark Energy Survey
(DES) and Wide-Field Infrared Survey Explorer (WISE). Images centered on these
galaxies were cut from the 1.85 arcmin resolution maps with frequency bands at
95, 150, and 220 GHz. The images were stacked, filtered, and fit with a
gray-body dust model to isolate the thermal Sunyaev-Zel'dovich (tSZ) signal,
which is proportional to the total energy contained in the CGM of the galaxies.
We separate these $M_{\star} = 10^{10.9} M_\odot$ - $10^{12} M_\odot$ galaxies
into 0.1 dex stellar mass bins, detecting tSZ per bin up to $5.6\sigma$ and a
total signal-to-noise ratio of $10.1\sigma$. We also detect dust with an
overall signal-to-noise ratio of $9.8\sigma$, which overwhelms the tSZ at
150GHz more than in other lower-redshift studies. We correct for the $0.16$ dex
uncertainty in the stellar mass measurements by parameter fitting for an
unconvolved power-law energy-mass relation, $E_{\rm therm} = E_{\rm therm,peak}
\left(M_\star/M_{\star,{\rm peak}} \right)^\alpha$, with the peak stellar mass
distribution of our selected galaxies defined as $M_{\star,{\rm peak}}= 2.3
\times 10^{11} M_\odot$. This yields an $E_{\rm therm,peak}=
5.98_{-1.00}^{+1.02} \times 10^{60}$ erg and $\alpha=3.77_{-0.74}^{+0.60}$.
These are consistent with $z \approx 0$ observations and within the limits of
moderate models of active galactic nuclei (AGN) feedback. We also compute the
radial profile of our full sample, which is similar to that recently measured
at lower-redshift by Schaan et al. (2021). | The spin of late-type galaxies at redshifts z < 1.2: We study the evolution of the galactic spin using data of high redshift
galaxies in the fields of the Great Observatories Origins Deep Survey (GOODS).
Through simple dynamical considerations we estimate the spin for the disc
galaxies in our sample and find that its distribution is consistent with that
found for nearby galaxies. Defining a dimensionless angular momentum parameter
for the disc component of the galaxies ($\lambda_{d}$), we do not find signs of
evolution in the redshift range $0.4 \leq z \leq 1.2$. We find that the mass
and environmental dependence of the spin of our high redshift galaxies are
similar to that of low-$z$ galaxies; showing a strong dependence on mass, in
the sense that low-mass systems present higher $\lambda_{d}$ values than
high-mass galaxies, with no significant dependence on the environmental
density. These results lead us to conclude that, although individual disc
galaxies might occasionally suffer from strong evolution, they evolve in such a
way that the overall spin distribution of the galactic population remains
constant from $z\sim1$ to the present epoch. |
Evolution of Cosmological Parameters and Fundamental Constants in a Flat
Quintessence Cosmology: A Dynamical Alternative to ΛCDM: The primary purpose of this work is the provision of accurate, analytic,
evolutionary templates for cosmological parameters and fundamental constants in
a dynamical cosmology. A flat quintessence cosmology with a dark energy
potential that has the mathematical form of the Higgs potential is the specific
cosmology and potential addressed in this work. These templates, based on the
physics of the cosmology and potential are intended to replace the
parameterizations currently used to determine the likelihoods of dynamical
cosmologies. Acknowledging that, unlike {\Lambda}CDM, the evolutions are
dependent on both the specific cosmology and the dark energy potential the
templates are referred to as Specific Cosmology and Potential, SCP, templates.
The requirements set for the SCP templates are that they must be accurate,
analytic functions of an observable such as the scale factor or redshift. This
is achieved through the utilization of a modified beta function formalism that
is based on a physically motivated dark energy potential to calculate the beta
function. The methodology developed here is designed to be adaptable to other
cosmologies and dark energy potentials. The SCP templates are essential tools
in determining the relative likelihoods of a range of dynamical cosmologies and
potentials. An ultimate purpose is the determination whether dark energy is
dynamical or static in a quantitative manner. It is suggested that the SCP
templates calculated in this work can serve as fiducial dynamical templates in
the same manner as {\Lambda}CDM serves for static dark energy. | The WiggleZ Dark Energy Survey: Improved Distance Measurements to z = 1
with Reconstruction of the Baryonic Acoustic Feature: We present significant improvements in cosmic distance measurements from the
WiggleZ Dark Energy Survey, achieved by applying the reconstruction of the
baryonic acoustic feature technique. We show using both data and simulations
that the reconstruction technique can often be effective despite patchiness of
the survey, significant edge effects and shot-noise. We investigate three
redshift bins in the redshift range 0.2<$z$<1, and in all three find
improvement after reconstruction in the detection of the baryonic acoustic
feature and its usage as a standard ruler. We measure model independent
distance measures $D_{\mathrm V}(r_{\mathrm s}^\mathrm{fid}/r_{\mathrm s})$ of
1716 $\pm$ 83 Mpc, 2221 $\pm$ 101 Mpc, 2516 $\pm$ 86 Mpc (68% CL) at effective
redshifts z = 0.44, 0.6, 0.73, respectively, where $D_{\mathrm V}$ is the
volume-average-distance, and $r_{\mathrm s}$ is the sound horizon at the end of
the baryon drag epoch. These significantly improved 4.8, 4.5 and 3.4 percent
accuracy measurements are equivalent to those expected from surveys with up to
2.5 times the volume of WiggleZ. These measurements are fully consistent with
cosmologies allowed by the analyses of the Planck Collaboration and the Sloan
Digital Sky Survey.We provide the $D_{\mathrm V}(r_{\mathrm
s}^\mathrm{fid}/r_{\mathrm s})$ posterior probability distributions and their
covariances. When combining these measurements with temperature fluctuations
measurements of Planck, the polarization of WMAP9, and the 6dF Galaxy Survey
baryonic acoustic feature, we do not detect deviations from a flat LCDM model.
Assuming this model we constrain the current expansion rate to $H_0$ = 67.15
$\pm$ 0.98 kms$^{-1}$Mpc$^{-1}$. Allowing the equation of state of dark energy
to vary we obtain $w_\mathrm{DE}$ = -1.080 $\pm$ 0.135. When assuming a curved
LCDM model we obtain a curvature value of $\Omega_{\mathrm K}$ = -0.0043 $\pm$
0.0047. |
Population III Star Formation in Magnetized Primordial Clouds: The evolution of primordial collapsing clouds and formation of
proto-Population III stars are investigated using three-dimensional ideal MHD
simulation. We calculated the evolution of magnetized primordial clouds from
the prestellar stage until the epoch after the proto-Population III star
formation, spatially resolving both parsec-scale clouds and sub-AU scale
protostars. The formation process of proto-population III star is characterized
by the ratio of rotational to magnetic energy of the parent cloud. When the
rotational energy is larger than the magnetic energy, fragmentation occurs in
the collapsing primordial cloud before the proto-Population III star formation
and binary or multiple system appears. Instead, when the magnetic energy is
larger than the rotational energy, strong jet with >100km s^-1 is driven by
circumstellar disk around the proto-population III star without fragmentation.
Thus, even in the early universe, the magnetic field plays an important role in
the star formation process. | A novel PBH production mechanism from non-Abelian gauge fields during
inflation: We consider the case of axion-like particles (ALPs) during inflation. When
coupled to a non-Abelian gauge sector via a Chern-Simons term, ALPs support an
intriguing, testable, phenomenology with very distinctive features including
chiral primordial gravitational waves. For sufficiently small values of the
gauge vev and coupling, scalar perturbations in the gauge sector exhibit a
known instability. We harness the power of such instability for primordial
black hole (PBH) generation. In the case of an axion-inflaton, one is
dynamically driven into a strong-backreaction regime that crosses the
instability band thereby sourcing a peaked scalar spectrum leading to PBH
production and the related scalar-induced gravitational waves. Remarkably, this
dynamics is largely insensitive to the initial conditions and the shape of the
potential, highlighting the universal nature of the sourcing mechanism. In the
case of spectator ALPs one can identify the parameter space that sets off the
strong backreaction regime and the ensuing features. We show that spectator ALP
models may also access the scalar instability region without triggering strong
backreaction. |
Pure Gravitational Wave Estimation of Hubble's Constant using Neutron
Star-Black Hole Mergers: Here we show how $H_0$ can be derived purely from the gravitational waves
(GW) of neutron star-black hole (NSBH) mergers. This new method provides an
estimate of $H_0$ spanning the redshift range, $z<0.25$ with current GW
sensitivity and without the need for any afterglow detection. We utilise the
inherently tight neutron star mass function together with the NSBH waveform
amplitude and frequency to estimate distance and redshift respectively, thereby
obtaining $H_0$ statistically. Our first estimate is $H_0 = 86^{+55}_{-46}$ km
s$^{-1}$ Mpc$^{-1}$ for the secure NSBH events GW190426 and GW200115. We
forecast that soon, with 10 more such NSBH events we can reach competitive
precision of $\delta H_0/H_0 \lesssim 20\%$. | The Relation between Nuclear Activity and Stellar Mass in Galaxies: The existence of correlations between nuclear properties of galaxies, such as
the mass of their central black holes, and larger scale features, like the
bulge mass and luminosity, represent a fundamental constraint on galaxy
evolution. Although the actual reasons for these relations have not yet been
identified, it is widely believed that they could stem from a connection
between the processes that lead to black hole growth and stellar mass assembly.
The problem of understanding how the processes of nuclear activity and star
formation can affect each other became known to the literature as the
Starburst-AGN connection. Despite years of investigation, the physical
mechanisms which lie at the basis of this relation are known only in part. In
this work, we analyze the problem of star formation and nuclear activity in a
large sample of galaxies. We study the relations between the properties of the
nuclear environments and of their host galaxies. We find that the mass of the
stellar component within the galaxies of our sample is a critical parameter,
that we have to consider in an evolutionary sequence, which provides further
insight in the connection between AGN and star formation processes. |
Suzaku Discovery of a Hard Component Varying Independently of the
Power-Law Emission in MCG-6-30-15: Focusing on hard X-ray variability, we reanalyzed Suzaku data of Type I
Seyfert galaxy MCG-6-30-15 obtained in 2006. Intensity-sorted spectroscopy and
a principal component analysis consistently revealed a very hard component that
varies independently of the dominant power-law emission. Although the exact
nature of this hard component is not yet identified, it can be modeled as a
power-law with a photon index ~2 affected by a partial covering absorption, or
as a thermal Comptonization emission with a relatively large optical depth.
When this component is included in the fitting model, the time-averaged 2.5-55
keV spectrum of MCG-6-30-15 can be reproduced successfully by invoking a mildly
broadened iron line with its emission region located at > 8 times the
gravitational radii from the central black hole, and a moderate reflection with
a covering fraction of ~3.4. This result implies that the solution of a highly
spinning black hole in MCG-6-30-15, obtained by Miniutti et al. (2007, PASJ,
59, S315) using the same Suzaku data, is a model dependent result. | Review on non-directional direct dark matter searches: An overview of non-directional direct detection methods is given. The
currently leading experiments for spin independent WIMPs interactions are using
simultaneous measurement of two quantities for event-by-event background
discrimination in cryogenic bolometers and noble gas like xenon. Besides these,
several interesting techniques have been developped, each having a specific
advantage concerning e.g energy threshold lowering or strong immunity to
ionizing radiations background. Technologies used and most recent results about
spin-dependent and spin-independent cases are presented. |
How unusual is the cool-core radio halo cluster CL1821+643 ?: Massive galaxy clusters with cool-cores typically host diffuse radio sources
called mini-haloes, whereas, those with non-cool-cores host radio haloes. We
attempt to understand the unusual nature of the cool-core galaxy cluster
CL1821+643 that hosts a Mpc-scale radio halo using new radio observations and
morphological analysis of its intra-cluster medium. We present the Giant
Metrewave Radio Telescope (GMRT) 610 MHz image of the radio halo. The spectral
index, $\alpha$ defined as $S\propto \nu^{-\alpha}$, of the radio halo is
$1.0\pm0.1$ over the frequency range of 323 - 610 - 1665 MHz. Archival {\it
Chandra} X-ray data were used to make surface brightness and temperature maps.
The morphological parameters Gini, $M_{20}$ and concentration ($C$) were
calculated on X-ray surface brightness maps by including and excluding the
central quasar (H1821+643) in the cluster. We find that the cluster CL1821+643,
excluding the quasar, is a non-relaxed cluster as seen in the morphological
parameter planes. It occupies the same region as other merging radio halo
clusters in the temperature- morphology parameter plane. We conclude that this
cluster has experienced a non-core-disruptive merger. | The SINS/zC-SINF survey of z~2 galaxy kinematics: Outflow properties: Based on SINFONI Ha, [NII] and [SII] AO data of 30 z \sim 2 star-forming
galaxies (SFGs) from the SINS and zcSINF surveys, we find a strong correlation
of the Ha broad flux fraction with the star formation surface density of the
galaxy, with an apparent threshold for strong outflows occurring at 1 Msun
yr^-1 kpc^-2. Above this threshold, we find that SFGs with logm_\ast>10 have
similar or perhaps greater wind mass loading factors (eta = Mdotout/SFR) and
faster outflow velocities than lower mass SFGs. This trend suggests that the
majority of outflowing gas at z \sim 2 may derive from high-mass SFGs, and that
the z \sim 2 mass-metallicity relation is driven more by dilution of enriched
gas in the galaxy gas reservoir than by the efficiency of outflows. The mass
loading factor is also correlated with the SFR and inclination, such that more
star-forming and face-on galaxies launch more powerful outflows. For galaxies
that have evidence for strong outflows, we find that the broad emission is
spatially extended to at least the half-light radius (\sim a few kpc). We
propose that the observed threshold for strong outflows and the observed mass
loading of these winds can be explained by a simple model wherein break-out of
winds is governed by pressure balance in the disk. Using the ratio of the [SII]
doublet in a broad and narrow component, we find that outflowing gas has a
density of \sim10-100 cm^-3, significantly less than that of the star forming
gas (600 cm^-3). |
Observability of Dark Matter Substructure with Pulsar Timing
Correlations: Dark matter substructure on small scales is currently weakly constrained, and
its study may shed light on the nature of the dark matter. In this work we
study the gravitational effects of dark matter substructure on measured pulsar
phases in pulsar timing arrays (PTAs). Due to the stability of pulse phases
observed over several years, dark matter substructure around the Earth-pulsar
system can imprint discernible signatures in gravitational Doppler and Shapiro
delays. We compute pulsar phase correlations induced by general dark matter
substructure, and project constraints for a few models such as monochromatic
primordial black holes (PBHs), and Cold Dark Matter (CDM)-like NFW subhalos.
This work extends our previous analysis, which focused on static or single
transiting events, to a stochastic analysis of multiple transiting events. We
find that stochastic correlations, in a PTA similar to the Square Kilometer
Array (SKA), are uniquely powerful to constrain subhalos as light as $\sim
10^{-13}~M_\odot$, with concentrations as low as that predicted by standard
CDM. | Planck 2015 results. XIII. Cosmological parameters: We present results based on full-mission Planck observations of temperature
and polarization anisotropies of the CMB. These data are consistent with the
six-parameter inflationary LCDM cosmology. From the Planck temperature and
lensing data, for this cosmology we find a Hubble constant, H0= (67.8 +/- 0.9)
km/s/Mpc, a matter density parameter Omega_m = 0.308 +/- 0.012 and a scalar
spectral index with n_s = 0.968 +/- 0.006. (We quote 68% errors on measured
parameters and 95% limits on other parameters.) Combined with Planck
temperature and lensing data, Planck LFI polarization measurements lead to a
reionization optical depth of tau = 0.066 +/- 0.016. Combining Planck with
other astrophysical data we find N_ eff = 3.15 +/- 0.23 for the effective
number of relativistic degrees of freedom and the sum of neutrino masses is
constrained to < 0.23 eV. Spatial curvature is found to be |Omega_K| < 0.005.
For LCDM we find a limit on the tensor-to-scalar ratio of r <0.11 consistent
with the B-mode constraints from an analysis of BICEP2, Keck Array, and Planck
(BKP) data. Adding the BKP data leads to a tighter constraint of r < 0.09. We
find no evidence for isocurvature perturbations or cosmic defects. The equation
of state of dark energy is constrained to w = -1.006 +/- 0.045. Standard big
bang nucleosynthesis predictions for the Planck LCDM cosmology are in excellent
agreement with observations. We investigate annihilating dark matter and
deviations from standard recombination, finding no evidence for new physics.
The Planck results for base LCDM are in agreement with BAO data and with the
JLA SNe sample. However the amplitude of the fluctuations is found to be higher
than inferred from rich cluster counts and weak gravitational lensing. Apart
from these tensions, the base LCDM cosmology provides an excellent description
of the Planck CMB observations and many other astrophysical data sets. |
Exponential growth of the number density of massive early-type galaxies: We determine the evolution of the co-moving density of the most massive ($M_*
\geq 10^{12} M_\odot$) early-type galaxy population in the redshift range of $z
= 0.15$ - 0.45 in different stellar mass ranges using data from the Sloan
Digital Sky Survey Data Release 7 (SDSS DR7) catalog. We find that the
co-moving number density of these galaxies grew exponentially, weakly depending
on the stellar mass range, as a function of cosmic time with a time-scale of
$\tau \simeq 1.16 \pm 0.16$ Gyr for at least 4 Gyr ending around $z \simeq
0.15$. This is about a factor of ten of growth between $z=0.5$ - 0.15. Since $z
\simeq 0.15$ a constant co-moving number density can be measured. According to
theoretical models the most massive early-type galaxies gain most of their
stellar mass via dry merging but the major merger rate measured by others
cannot account for the high growth in number density we measured thus, stellar
mass gain from minor mergers and slow, smooth accretion seems to play an
important role. We outline a simple analytic model that explains the observed
evolution based on the exponential decline of the luminosity function and sets
constraints on the time dependence of the close-pair fraction of merger
candidate galaxies. | Variable time flow as an alternative to dark energy: Time is a parameter playing a central role in our most fundamental modelling
of natural laws. Relativity theory shows that the comparison of times measured
by different clocks depends on their relative motions and on the strength of
the gravitational field in which they are embedded. In standard cosmology, the
time parameter is the one measured by fundamental clocks, i.e. clocks at rest
with respect to the expanding space. This proper time is assumed to flow at a
constant rate throughout the whole history of the Universe. We make the
alternative hypothesis that the rate at which cosmological time flows depends
on the global geometric curvature the Universe. Using a simple one-parameter
model for the relation between proper time and curvature, we build a
cosmological model that fits the Type Ia Supernovae data (the best cosmological
standard candles) without the need for dark energy nor probably exotic dark
matter. |
Quasars probing intermediate redshift star-forming galaxies: We present a sample of 46 [OIII]-emitting galaxies at z<0.8 detected in the
fibre spectra of quasars from the SDSS-DR7 through an automatic search
procedure. We also detect [OII] and Hb emission lines from most of these
galaxies in the SDSS spectra. We study both the emission and absorption
properties of a sub-sample of 17 galaxies in the redshift range z=0.4-0.7,
where MgII lines are covered by the SDSS spectra. The measured lower-limits on
the star-formation rates of these galaxies are in the range 0.2-20 M_sun/yr.
The emission line luminosities and (O/H) metallicities from R23 measured in
this sample are similar to what is found in normal galaxies at these redshifts.
Thus, this constitutes a unique sample of intermediate redshift star-forming
galaxies where we can study the QSO absorber - galaxy connection. Strong MgII
(W>1A) as well as MgI absorption lines are detected in the QSO spectra at the
redshift of most of these galaxies. Strong FeII (W>1A) absorption lines are
also generally detected whenever the appropriate wavelength ranges are covered.
This suggests that most of these systems could be bona-fide Damped Lyman-alpha
systems. We investigate various possible relations between the MgII rest
equivalent widths and the emission line properties. We find a possible (2
sigma) correlation between the emission-line metallicity of the galaxies and
the MgII rest equivalent width of the absorbers [truncated]. | Cosmology today-A brief review: This is a brief review of the standard model of cosmology. We first introduce
the FRW models and their flat solutions for energy fluids playing an important
role in the dynamics at different epochs. We then introduce different
cosmological lengths and some of their applications. The later part is
dedicated to the physical processes and concepts necessary to understand the
early and very early Universe and observations of it. |
The Imprint of The Extragalactic Background Light in the Gamma-Ray
Spectra of Blazars: The light emitted by stars and accreting compact objects through the history
of the Universe is encoded in the intensity of the extragalactic background
light (EBL). Knowledge of the EBL is important to understand the nature of star
formation and galaxy evolution, but direct measurements of the EBL are lim-
ited by Galactic and other foreground emissions. Here we report an absorption
feature seen in the combined spectra of a sample of gamma-ray blazars out to a
redshift of z$\sim$1.6. This feature is caused by attenuation of gamma rays by
the EBL at optical to UV frequencies, and allowed us to measure the EBL flux
density in this frequency band. | A Lyman alpha halo around a quasar at redshift z=6.4: We present long-slit spectroscopic data which reveals extended Lyman alpha
emission around the z=6.417 radio-quiet quasar CFHQS J2329-0301. The Lyman
alpha emission is extended over 15 kpc and has a luminosity of > 8 x 10^36 W,
comparable to the most luminous Lyman alpha halos known. The emission has
complex kinematics, in part due to foreground absorption which only partly
covers the extended nebula. The velocity ranges from -500 km/s to +500 km/s,
with a peak remarkably close to the systemic velocity identified by broad MgII
emission of the quasar. There is no evidence for infall or outflow of the halo
gas. We speculate that the Lyman alpha emission mechanism is recombination
after quasar photo-ionization of gas sitting within a high-mass dark matter
halo. The immense Lyman alpha luminosity indicates a higher covering factor of
cold gas compared to typical radio-quiet quasars at lower redshift. |
Careful calculation of thermodynamical functions of tachyon gas: We analyze several approaches to the thermodynamics of tachyon matter. The
energy spectrum of tachyons $\epsilon_k=\sqrt{k^2-m^2}$ is defined at $k\geq m$
and it is not evident how to determine the tachyonic distribution function and
calculate its thermodynamical parameters. Integrations within the range $k\in
(m,\infty) $ yields no imaginary quantities and tachyonic thermodynamical
functions at zero temperature satisfy the third law of thermodynamics. It is
due to an anomalous term added to the pressure. This approach seems to be
correct, however, exact analysis shows that the entropy may become negative at
finite temperature. The only right choice is to perform integration within the
range $k\in (0,\infty) $, taking extended distribution function $f_\epsilon =1$
and the energy spectrum $\epsilon_k=0$ when $k<m$. No imaginary quantity
appears and the entropy reveals good behavior. The anomalous pressure of
tachyons vanishes but this concept may play very important role in the
thermodynamics of other forms of exotic matter. | Cosmology with SKA Radio Continuum Surveys: Radio continuum surveys have, in the past, been of restricted use in
cosmology. Most studies have concentrated on cross-correlations with the cosmic
microwave background to detect the integrated Sachs-Wolfe effect, due to the
large sky areas that can be surveyed. As we move into the SKA era, radio
continuum surveys will have sufficient source density and sky area to play a
major role in cosmology on the largest scales. In this chapter we summarise the
experiments that can be carried out with the SKA as it is built up through the
coming decade. We show that the SKA can play a unique role in constraining the
non-Gaussianity parameter to \sigma(f_NL) ~ 1, and provide a unique handle on
the systematics that inhibit weak lensing surveys. The SKA will also provide
the necessary data to test the isotropy of the Universe at redshifts of order
unity and thus evaluate the robustness of the cosmological principle.Thus, SKA
continuum surveys will turn radio observations into a central probe of
cosmological research in the coming decades. |
Major Merging: The Way to Make a Massive, Passive Galaxy: We analyze the projected axial ratio distribution, p(b/a), of galaxies that
were spectroscopically selected from the Sloan Digital Sky Survey (DR6) to have
low star-formation rates. For these quiescent galaxies we find a rather abrupt
change in p(b/a) at a stellar mass of ~10^{11} M_sol: at higher masses there
are hardly any galaxies with b/a<0.6, implying that essentially none of them
have disk-like intrinsic shapes and must be spheroidal. This transition mass is
~3-4 times higher than the threshold mass above which quiescent galaxies
dominate in number over star-forming galaxies, which suggests these mass scales
are unrelated. At masses lower than ~10^{11} M_sol, quiescent galaxies show a
large range in axial ratios, implying a mix of bulge- and disk-dominated
galaxies. Our result strongly suggests that major merging is the most
important, and perhaps only relevant, evolutionary channel to produce massive
(>10^{11} M_sol), quiescent galaxies, as it inevitably results in spheroids. | The Cosmic Microwave Background: The history of its experimental
investigation and its significance for cosmology: This review describes the discovery of the cosmic microwave background
radiation in 1965 and its impact on cosmology in the 50 years that followed.
This discovery has established the Big Bang model of the Universe and the
analysis of its fluctuations has confirmed the idea of inflation and led to the
present era of precision cosmology. I discuss the evolution of cosmological
perturbations and their imprint on the CMB as temperature fluctuations and
polarization. I also show how a phase of inflationary expansion generates
fluctuations in the spacetime curvature and primordial gravitational waves. In
addition I present findings of CMB experiments, from the earliest to the most
recent ones. The accuracy of these experiments has helped us to estimate the
parameters of the cosmological model with unprecedented precision so that in
the future we shall be able to test not only cosmological models but General
Relativity itself on cosmological scales. |
Crossing $w=-1$ by a single scalar field coupling with matter and the
observational constraints: Motivated by Yang-Mills dark energy model, we propose a new model by
introducing a logarithmic correction. we find that this model can avoid the
coincidence problem naturally and gives an equation of state $w$ smoothly
crossing -1 if an interaction between dark energy and dark matter exists. It
has a stable tracker solution as well. To confront with observations based on
the combined data of SNIa, BAO, CMB and Hubble parameter, we obtain the best
fit values of the parameters with $1\sigma, 2\sigma, 3\sigma$ errors for the
noncoupled model: $\Omega_m=0.276\pm0.008^{+0.016+0.024}_{-0.015-0.022}$,
$h=0.699\pm0.003\pm0.006\pm0.008$, and for the coupled model with a decaying
rate $\gamma=0.2$: $\Omega_m=0.291\pm0.004^{+0.008+0.012}_{-0.007-0.011}$,
$h=0.701\pm0.002\pm0.005\pm0.007$. In particular, it is found that the
non-coupled model has a dynamic evolution almost undistinguishable to
$\Lambda$CDM at the late-time Universe. | Are Newly Discovered HI High Velocity Clouds Minihalos in the Local
Group?: A set of HI sources extracted from the north Galactic polar region by the
ongoing ALFALFA survey has properties that are consistent with the
interpretation that they are associated with isolated minihalos in the
outskirts of the Local Group (LG). Unlike objects detected by previous surveys,
such as the Compact High Velocity Clouds of Braun & Burton (1999), the HI
clouds found by ALFALFA do not violate any structural requirements or halo
scaling laws of the LambdaCDM structure paradigm, nor would they have been
detected by extant HI surveys of nearby galaxy groups other than the LG. At a
distance of d Mpc, their HI masses range between $5 x 10^4 d^2 and 10^6 d^2
solar and their HI radii between <0.4d and 1.6 d kpc. If they are parts of
gravitationally bound halos, the total masses would be on order of 10^8--10^9
solar, their baryonic content would be signifcantly smaller than the cosmic
fraction of 0.16 and present in a ionized gas phase of mass well exceeding that
of the neutral phase. This study does not however prove that the minihalo
interpretation is unique. Among possible alternatives would be that the clouds
are shreds of the Leading Arm of the Magellanic Stream. |
Current cosmological constraints on the curvature, dark energy and
modified gravity: We apply the Union2 compilation of 557 supernova Ia data, the baryon acoustic
oscillation measurement of distance, the cosmic microwave background radiation
data from the seven year Wilkinson Microwave Anisotropy Probe, and the Hubble
parameter data to study the geometry of the Universe and the property of dark
energy by using models and parametrizations with different high redshift
behaviours of $w(z)$. We find that $\Lambda$CDM model is consistent with
current data, that the Dvali-Gabadadze-Porrati model is excluded by the data at
more than $3\sigma$ level, that the Universe is almost flat, and that the
current data is unable to distinguish models with different behaviours of
$w(z)$ at high redshift. We also add the growth factor data to constrain the
growth index of Dvali-Gabadadze-Porrati model and find that it is more than
$1\sigma$ away from its theoretical value. | Ionized Gas in the Irr Galaxy IC 10: The Emission Spectrum and
Ionization Sources: We present the results of observations of the Irr galaxy IC 10 at the 6-m SAO
telescope with the panoramic Multi-Pupil Fiber Spectrograph (MPFS). Based on
the results of these observations and our long-slit spectroscopy performed
previously, we have investigated the ionized-gas emission spectrum in the
region of intense star formation and refined the gas metallicity estimates. We
show that the "diagnostic diagrams" constructed from our observations agree
best with the new improved ionization models by Martin-Manjon et al. Using
these models, we have determined the electron density and gas ionization
parameter and ionizing-cluster characteristics, the age and mass, from the
spectra of the investigated HII regions. The cluster age and mass are shown to
be within the ranges 2.5 - 5 Myr and (0.2 - 1)*10^5 M(sun), respectively. |
X-ray emission from cosmic web filaments in SRG/eROSITA data: Using the publicly available eROSITA Final Equatorial Depth Survey (eFEDS)
data, we detected the stacked X-ray emissions at the position of 463 filaments
at a significance of 3.8 sigma based on the combination of all energy bands. In
parallel, we found that the probability of the measurement under the null
hypothesis is ~0.0017. The filaments were identified with galaxies in the Sloan
Digital Sky Survey survey, ranging from 30 Mpc to 100 Mpc in length at 0.2 < z
< 0.6. The stacking of the filaments was performed with the eFEDS X-ray
count-rate maps in the energy range between 0.4 - 2.3 keV after masking the
resolved galaxy groups and clusters and the identified X-ray point sources from
the ROSAT, Chandra, XMM-Newton, and eROSITA observations. In addition, diffuse
X-ray foreground and background emissions or any residual contribution were
removed by subtracting the signal in the region between 10 - 20 Mpc from the
filament spines. For the stacked signal, we performed an X-ray spectral
analysis, which indicated that the signal is associated with a thermal
emission. According to a model with the astrophysical plasma emission code for
the plasma emission and with a beta-model gas distribution with beta=2/3, the
detected X-ray signal can be interpreted as emission from hot gas in the
filaments with an average gas temperature of 1.0 (+0.3 -0.2) keV and a gas
overdensity of 21 +- 5 at the center of the filaments. | A cosmic microwave background search for fine-structure constant
evolution: In some extensions of the standard model of particle physics, the values of
the fundamental coupling constants vary in space and time. Some observations of
quasars hint at time and spatial variation of the fine structure constant
$\alpha$. Here, the Bekenstein-Sandvik-Barrow-Magueijo (BSBM) model (which
posits the existence of a scalar field driving evolution in the fundamental
electric charge $e$) is tested against quasar and Planck satellite cosmic
microwave background (CMB) data. In this model, variations in $e$ are coupled
to the matter density through a factor $\zeta_{\rm m}/{\omega}$, which is
related to electromagnetic contributions to nucleon masses, and {the energy}
scale of new physics. Simulations conducted here do not support claims that the
electrostatic contribution to $\zeta_{m}$ is completely shielded. Other common
approximations used in BSBM field evolution are found to be adequate. Principal
components of the CMB data with respect to variations in $\alpha$ are used to
obtain constraints of $\zeta_{\rm m}/{\omega}\lesssim 9.3 \times 10^{-9}$ for a
massless field. A forecast anticipating the promise of the Simons Observatory
(SO) CMB experiment shows that SO will be sensitive to values of $\zeta_{\rm
m}/{\omega}\geq 2.2 \times 10^{-9}$. |
Weak-Lensing Mass Calibration of ACTPol Sunyaev-Zel'dovich Clusters with
the Hyper Suprime-Cam Survey: We present weak-lensing measurements using the first-year data from the Hyper
Suprime-Cam Strategic Survey Program on the Subaru telescope for eight galaxy
clusters selected through their thermal Sunyaev-Zel'dovich (SZ) signal measured
at 148 GHz with the Atacama Cosmology Telescope Polarimeter experiment. The
overlap between the two surveys in this work is 33.8 square degrees, before
masking bright stars. The signal-to-noise ratio of individual cluster lensing
measurements ranges from 2.2 to 8.7, with a total of 11.1 for the stacked
cluster weak-lensing signal. We fit for an average weak-lensing mass
distribution using three different profiles, a Navarro-Frenk-White profile, a
dark-matter-only emulated profile, and a full cosmological hydrodynamic
emulated profile. We interpret the differences among the masses inferred by
these models as a systematic error of 10\%, which is currently smaller than the
statistical error. We obtain the ratio of the SZ-estimated mass to the
lensing-estimated mass (the so-called hydrostatic mass bias $1-b$) of
$0.74^{+0.13}_{-0.12}$, which is comparable to previous SZ-selected clusters
from the Atacama Cosmology Telescope and from the {\sl Planck} Satellite. We
conclude with a discussion of the implications for cosmological parameters
inferred from cluster abundances compared to cosmic microwave background
primary anisotropy measurements. | The sub-mm morphology of the interacting galaxy NGC 3627: We present sub-mm continuum and heterodyne data of the interacting galaxy NGC
3627, obtained with the HHT and APEX. We find significant changes in the
molecular line ratios over small scales in the southeastern part of this
galaxy. The kinematics of the CO(2-1) line, as well as the morphology in the
870um continuum emission, suggest a continuation of the western spiral arm on
the east side of the galaxy's central area. This continued spiral arm crosses
the normal eastern spiral arm in an area which shows an unusual magnetic field
configuration. This spiral arm crossing, independently of if it's physical or
just projected, may help in the understanding of the observed magnetic field
configuration. |
Search for cold and hot gas in the ram pressure stripped Virgo dwarf
galaxy IC3418: We present IRAM 30m sensitive upper limits on CO emission in the ram pressure
stripped dwarf Virgo galaxy IC3418 and in a few positions covering HII regions
in its prominent 17 kpc UV/Ha gas-stripped tail. In the central few arcseconds
of the galaxy, we report a possible marginal detection of about 1x10^6 M_sun of
molecular gas (assuming a Galactic CO-to-H_2 conversion factor) that could
correspond to a surviving nuclear gas reservoir. We estimate that there is less
molecular gas in the main body of IC3418, by at least a factor of 20, than
would be expected from the pre-quenching UV-based star formation rate assuming
the typical gas depletion timescale of 2 Gyr. Given the lack of star formation
in the main body, we think the H_2-deficiency is real, although some of it may
also arise from a higher CO-to-H_2 factor typical in low-metallicity, low-mass
galaxies. The presence of HII regions in the tail of IC3418 suggests that there
must be some dense gas; however, only upper limits of < 1x10^6 M_sun were found
in the three observed points in the outer tail. This yields an upper limit on
the molecular gas content of the whole tail < 1x10^7 M_sun, which is an amount
similar to the estimates from the observed star formation rate over the tail.
We also present strong upper limits on the X-ray emission of the stripped gas
in IC3418 from a new Chandra observation. The measured X-ray luminosity of the
IC3418 tail is about 280 times lower than that of ESO 137-001, a spiral galaxy
in a more distant cluster with a prominent ram pressure stripped tail.
Non-detection of any diffuse X-ray emission in the IC3418 tail may be due to a
low gas content in the tail associated with its advanced evolutionary state
and/or due to a rather low thermal pressure of the surrounding intra-cluster
medium. | Large HI optical depth and Redshifted 21-cm signal from cosmic dawn: The HI 21-cm optical depth ($\tau_b$) can be considerably large as the
kinetic and spin temperature of the inter-galactic medium (IGM) is expected to
be very low during cosmic dawn. It will be particularly higher at regions with
HI over-density. We revisit the validity of the widely used linearized equation
for estimating the HI 21-cm differential brightness temperature ($T_b$) which
assumes $\tau_b << 1$ and approximates $[1-\exp({-\tau_b})]$ as $\tau_b$. We
consider two scenarios, one without any additional cooling mechanism or radio
background (referred as the standard scenario) and the other (referred as the
excess-cooling} scenario) assumes the EDGES-like absorption profile and an
excess cooling mechanism. We find that given a measured global absorption
signal, consistent with the standard (excess-cooling) scenario, the linearized
equation overestimates the spin temperature by $\sim 5\%(10\%)$. Further, using
numerical simulations, we study the impact that the large optical depth has on
various signal statistics. We observe that the variance, skewness and kurtosis,
calculated at simulation resolution ($\sim 0.5 h^{-1} \, {\rm Mpc}$), are
over-predicted up to $\sim 30\%$, $30\%$ and $15\%$ respectively for the
standard and up to $\sim 90\%$, $50\%$ and $50\%$ respectively for the
excess-cooling scenario. Moreover, we find that the probability distribution
function of $T_b$ is squeezed and becomes more Gaussian in shape if no
approximation is made. The spherically averaged HI power spectrum is
overpredicted by up to $\sim 25 \%$ and $80\%$ at all scales for the standard
and excess-cooling scenarios respectively. |
Galaxy cluster searches based on photometric redshifts in the four
CFHTLS Wide fields: We have developed a method for detecting clusters in large imaging surveys,
based on the detection of structures in galaxy density maps made in slices of
photometric redshifts. This method was first applied to the Canada France
Hawaii Telescope Legacy Survey (CFHTLS) Deep 1 field by Mazure et al. (2007),
then to all the Deep and Wide CFHTLS fields available in the T0004 data release
by Adami et al. (2010). The validity of the cluster detection rate was
estimated by applying the same procedure to galaxies from the Millennium
simulation. Here we analyse with the same method the full CFHTLS Wide survey,
based on the T0006 data release. In a total area of 154 deg2, we have detected
4061 candidate clusters at 3sigma or above (6802 at 2sigma and above), in the
redshift range 0.1<=z<=1.15, with estimated mean masses between 1.3 10^14 and
12.6 10^14 M_solar. This catalogue of candidate clusters will be available
online via VizieR. We compare our detections with those made in various CFHTLS
analyses with other methods. By stacking a subsample of clusters, we show that
this subsample has typical cluster characteristics (colour-magnitude relation,
galaxy luminosity function). We also confirm that the cluster-cluster
correlation function is comparable to that obtained for other cluster surveys
and analyze large scale filamentary galaxy distributions. We have increased the
number of known optical high redshift cluster candidates by a large factor, an
important step towards obtaining reliable cluster counts to measure
cosmological parameters. The clusters that we detect behave as expected for a
sample of clusters fed by filaments at the intersection of which they are
located. | Blind correction of the EB-leakage in the pixel domain: We study the problem of EB-leakage that is associated with incomplete
polarized CMB sky. In the blind case that assumes no additional information
about the statistical properties and amplitudes of the signal from the missing
sky region, we prove that the recycling method (Liu et al.~2018) gives the
unique best estimate of the EB-leakage. Compared to the previous method, this
method reduces the uncertainties in the BB power spectrum due to EB-leakage by
more than one order of magnitude in the most interesting domain of multipoles,
where $\ell$ is between $80$ and $200$. This work also provides a useful
guideline for observational design of future CMB experiments. |
Testing bound dark energy with cosmological parameter and fundamental
constant evolution: A new bound dark energy, BDE, cosmology has been proposed where the dark
energy is the binding energy between light meson fields that condense a few
tens of years after the big bang. It is reported that the correct dark energy
density emerges using particle physics without fine tuning. This alone makes
the BDE cosmology worthy of further investigation. This work looks at the late
time BDE predictions of the evolution of cosmological parameters and the values
of fundamental constants to determine whether the cosmology's predictions are
consistent with observation. The work considers the time period between a scale
factor of 0.1 and 1.0. A model BDE cosmology is considered with current day
values of the cosmological parameters well within the observational limits. The
calculations use three different values of the current day dark energy equation
of state close to minus one. All three cases produce evolutions of the
cosmological parameters and fundamental constants consistent with the
observational constraints. Analytic relations between the BDE and cosmological
parameters are developed to insure a consistent set of parameters. | Imaging Systematics and Clustering of DESI Main Targets: We evaluate the impact of imaging systematics on the clustering of luminous
red galaxies (LRG), emission-line galaxies (ELG) and quasars (QSO) targeted for
the upcoming Dark Energy Spectroscopic Instrument (DESI) survey. Using Data
Release 7 of the DECam Legacy Survey, we study the effects of astrophysical
foregrounds, stellar contamination, differences between north galactic cap and
south galactic cap measurements, and variations in imaging depth, stellar
density, galactic extinction, seeing, airmass, sky brightness, and exposure
time before presenting survey masks and weights to mitigate these effects. With
our sanitized samples in hand, we conduct a preliminary analysis of the
clustering amplitude and evolution of the DESI main targets. From measurements
of the angular correlation functions, we determine power law fits $r_0 = 7.78
\pm 0.26$ $h^{-1}$Mpc, $\gamma = 1.98 \pm 0.02$ for LRGs and $r_0 = 5.45 \pm
0.1$ $h^{-1}$Mpc, $\gamma = 1.54 \pm 0.01$ for ELGs. Additionally, from the
angular power spectra, we measure the linear biases and model the scale
dependent biases in the weakly nonlinear regime. Both sets of clustering
measurements show good agreement with survey requirements for LRGs and ELGs,
attesting that these samples will enable DESI to achieve precise cosmological
constraints. We also present clustering as a function of magnitude, use
cross-correlations with external spectroscopy to infer $dN/dz$ and measure
clustering as a function of luminosity, and probe higher order clustering
statistics through counts-in-cells moments. |
Modeling The GRB Host Galaxy Mass Distribution: Are GRBs Unbiased
Tracers of Star Formation?: We model the mass distribution of long gamma-ray burst (GRB) host galaxies
given recent results suggesting that GRBs occur in low metallicity
environments. By utilizing measurements of the redshift evolution of the
mass-metallicity (M-Z) relationship for galaxies, along with a sharp host
metallicity cut-off suggested by Modjaz and collaborators, we estimate an upper
limit on the stellar mass of a galaxy that can efficiently produce a GRB as a
function of redshift. By employing consistent abundance indicators, we find
that sub-solar metallicity cut-offs effectively limit GRBs to low stellar mass
spirals and dwarf galaxies at low redshift. At higher redshifts, as the average
metallicity of galaxies in the Universe falls, the mass range of galaxies
capable of hosting a GRB broadens, with an upper bound approaching the mass of
even the largest spiral galaxies. We compare these predicted limits to the
growing number of published GRB host masses and find that extremely low
metallicity cut-offs of 0.1 to 0.5 solar are effectively ruled out by a large
number of intermediate mass galaxies at low redshift. A mass function that
includes a smooth decrease in the efficiency of producing GRBs in galaxies of
metallicity above 12+log(O/H)_(KK04) ~ 8.7 can, however, accommodate a majority
of the measured host galaxy masses. We find that at z ~ 1, the peak in the
observed GRB host mass distribution is inconsistent with the expected peak in
the mass of galaxies harboring most of the star formation. This suggests that
GRBs are metallicity biased tracers of star formation at low and intermediate
redshifts, although our model predicts that this bias should disappear at
higher redshifts due to the evolving metallicity content of the universe. | Round Table Discussion at the Workshop "New Directions in Modern
Cosmology": The workshop "New directions in modern cosmology", organized by Theo
Nieuwenhuizen, Rudy Schild, Francesco Sylos Labini and Ruth Durrer, was held
from September 27 until October 1, 2010, in the Lorentz Center in Leiden, the
Netherlands. A transcript of the final round table discussion, chaired by Theo
Nieuwenhuizen and Rudy Schild, is presented. The subjects are: 0) spread in
data; 1) back reaction; 2) $N$-body simulations; 3) neutrinos as the dark
matter; 4) gravitational hydrodynamics, 5) missing baryons and lensing in an
inhomogeneous universe, and 6) final points. |
Abundance determination in HII regions from spectra without the
[OII]3727+3729 line: We suggest an empirical calibration for determination of oxygen and nitrogen
abundances and electron temperature in HII regions where the [OII]3727+3729
line (R_2) is not available. The calibration is based on the strong emission
lines of OIII, NII, and SII (NS calibration) and derived using the spectra of
HII regions with measured electron temperatures as calibration datapoints. The
NS calibration makes it possible to derive abundances for HII regions in nearby
galaxies from the SDSS spectra where R_2 line is out of the measured wavelength
range, but can also be used for the oxygen and nitrogen abundances
determinations in any HII region independently whether the nebular oxygen line
[OII]3727+3729 is available or not. The NS calibration provides reliable oxygen
and nitrogen abundances for HII regions over the whole range of metallicities. | Fractal Dimension as a measure of the scale of Homogeneity: In the multi-fractal analysis of large scale matter distribution, the scale
of transition to homogeneity is defined as the scale above which the fractal
dimension of underlying point distribution is equal to the ambient dimension of
the space in which points are distributed. With finite sized weakly clustered
distribution of tracers obtained from galaxy redshift surveys it is difficult
to achieve this equality. Recently we have defined the scale of homogeneity to
be the scale above which the deviation of fractal dimension from the ambient
dimension becomes smaller than the statistical dispersion. In this paper we use
the relation between the fractal dimensions and the correlation function to
compute the dispersion for any given model in the limit of weak clustering
amplitude. We compare the deviation and dispersion for the LCDM model and
discuss the implication of this comparison for the expected scale of
homogeneity in the concordant model of cosmology. We estimate the upper limit
to the scale of homogeneity to be close to 260 Mpc/h for the LCDM model. Actual
estimates of the scale of homogeneity should be smaller than this as we have
considered only statistical contribution to the dispersion in fractal dimension
and we have ignored cosmic variance and contributions due to survey geometry
and the selection function. We find that as long as non linear correction are
insignificant, scale of homogeneity as defined above does not change with
epoch. The scale of homogeneity depends very weakly on the choice of tracer of
the density field. Thus the suggested definition of the scale of homogeneity is
fairly robust. |
Gaussian Process Regression for foreground removal in HI intensity
mapping experiments: We apply for the first time Gaussian Process Regression (GPR) as a foreground
removal technique in the context of single-dish, low redshift HI intensity
mapping, and present an open-source Python toolkit for doing so. We use MeerKAT
and SKA1-MID-like simulations of 21cm foregrounds (including polarisation
leakage), HI cosmological signal and instrumental noise. We find that it is
possible to use GPR as a foreground removal technique in this context, and that
it is better suited in some cases to recover the HI power spectrum than
Principal Component Analysis (PCA), especially on small scales. GPR is
especially good at recovering the radial power spectrum, outperforming PCA when
considering the full bandwidth of our data. Both methods are worse at
recovering the transverse power spectrum, since they rely on frequency-only
covariance information. When halving our data along frequency, we find that GPR
performs better in the low frequency range, where foregrounds are brighter. It
performs worse than PCA when frequency channels are missing, to emulate RFI
flagging. We conclude that GPR is an excellent foreground removal option for
the case of single-dish, low redshift HI intensity mapping in the absence of
missing frequency channels. Our Python toolkit gpr4im and the data used in this
analysis are publicly available on GitHub. | Rotation curves of rotating galactic BEC dark matter halos: We present the dynamics of rotating Bose Condensate galactic dark matter
halos, made of an ultralight spinless boson. We restrict to the case of adding
axisymmetric rigid rotation to initially spherically symmetric structures and
show there are three regimes: i) small angular momentum, that basically retains
the drawbacks of spherically symmetric halos related to compactness and failure
at explaining galactic RCs, ii) an intermediate range of values of angular
momentum that allow the existence of long-lived structures with acceptable RC
profiles, and iii) high angular momentum, in which the structure is dispersed
away by rotation. We also present in detail the new code used to solve the
Gross-Pitaevskii Poisson system of equations in three dimensions. |
Gravitational Lens Recovery with GLASS: Measuring the mass profile and
shape of a lens: We use a new non-parametric gravitational modelling tool -- \Glass{} -- to
determine what quality of data (strong lensing, stellar kinematics, and/or
stellar masses) are required to measure the circularly averaged mass profile of
a lens and its shape. \Glass{} uses an under-constrained adaptive grid of mass
pixels to model the lens, searching through thousands of models to marginalise
over model uncertainties. Our key findings are as follows: (i) for pure lens
data, multiple sources with wide redshift separation give the strongest
constraints as this breaks the well-known mass-sheet or steepness degeneracy;
(ii) a single quad with time delays also performs well, giving a good recovery
of both the mass profile and its shape; (iii) stellar masses -- for lenses
where the stars dominate the central potential -- can also break the steepness
degeneracy, giving a recovery for doubles almost as good as having a quad with
time delay data, or multiple source redshifts; (iv) stellar kinematics provide
a robust measure of the mass at the half light radius of the stars $r_{1/2}$
that can also break the steepness degeneracy if the Einstein radius $r_E \neq
r_{1/2}$; and (v) if $r_E \sim r_{1/2}$, then stellar kinematic data can be
used to probe the stellar velocity anisotropy $\beta$ -- an interesting
quantity in its own right. Where information on the mass distribution from
lensing and/or other probes becomes redundant, this opens up the possibility of
using strong lensing to constrain cosmological models. | Inflationary magnetogenesis with a self-consistent coupling function: In this paper, we discuss the inflationary magnetogenesis scenario, in which
the coupling function is introduced to break the conformal invariance of
electromagnetic action. Unlike in conventional models, we deduce the Maxwell's
equations under the perturbed FRW metric. We found that, the self-consistency
of the action depends on the form of the coupling function when the scalar mode
perturbations have been considered. Therefore, this self-consistency can be
seen as a restriction on the coupling function. In this paper, we give the
restrictive equation for coupling function then obtain the specific form of the
coupling function in a simple model. We found that the coupling function
depends on the potential of the inflaton and thus is model dependent. We obtain
the power spectrum of electric field and magnetic field in large-field
inflation model. We also found that the coupling function is a incresing
function of time during slow-roll era as most of inflationary magnetogenesis
models, it will lead to strong coupling problem. This issue is discussed
qualitatively by introducing a correction function during the preheating. |
Spectroscopic identification of a redshift 1.55 supernova host galaxy
from the Subaru Deep Field Supernova Survey: Context: The Subaru Deep Field (SDF) Supernova Survey discovered 10 Type Ia
supernovae (SNe Ia) in the redshift range 1.5<z<2.0, as determined solely from
photometric redshifts of the host galaxies. However, photometric redshifts
might be biased, and the SN sample could be contaminated by active galactic
nuclei (AGNs).
Aims: We aim to obtain the first robust redshift measurement and
classification of a z > 1.5 SDF SN Ia host galaxy candidate
Methods: We use the X-shooter (U-to-K-band) spectrograph on the Very Large
Telescope to allow the detection of different emission lines in a wide spectral
range.
Results: We measure a spectroscopic redshift of 1.54563 +/- 0.00027 of
hSDF0705.25, consistent with its photometric redshift of 1.552 +/- 0.018. From
the strong emission-line spectrum we rule out AGN activity, thereby confirming
the optical transient as a SN. The host galaxy follows the fundamental
metallicity relation defined in Mannucci et al. (2010, 2011) showing that the
properties of this high-redshift SN Ia host galaxy is similar to other field
galaxies.
Conclusions: Spectroscopic confirmation of additional SDF SN hosts would be
required to confirm the cosmic SN rate evolution measured in the SDF. | Effects of Lens Motion and Uneven Magnification on Image Spectra: Counter to intuition, the images of an extended galaxy lensed by a moving
galaxy cluster should have slightly different spectra in any metric gravity
theory. This is mainly for two reasons. One relies on the gravitational
potential of a moving lens being time-dependent (the $\text{Moving}$
$\text{Cluster}$ $\text{Effect}$, $\text{MCE}$). The other is due to uneven
magnification across the extended, rotating source (the $\text{Differential}$
$\text{Magnification}$ $\text{Effect}$, $\text{DME}$). The time delay between
the images can also cause their redshifts to differ because of cosmological
expansion. This Differential Expansion Effect is likely to be small. Using a
simple model, we derive these effects from first principles.
One application would be to the Bullet Cluster, whose large tangential
velocity may be inconsistent with the $\Lambda CDM$ paradigm. This velocity can
be estimated with complicated hydrodynamic models. Uncertainties with such
models can be avoided using the MCE. We argue that the MCE should be observable
with ALMA.
However, such measurements can be corrupted by the DME if typical spiral
galaxies are used as sources. Fortunately, we find that if detailed spectral
line profiles were available, then the DME and MCE could be distinguished. It
might also be feasible to calculate how much the DME should affect the mean
redshift of each image. Resolved observations of the source would be required
to do this accurately.
The DME is of order the source angular size divided by the Einstein radius
times the redshift variation across the source. Thus, it mostly affects nearly
edge-on spiral galaxies in certain orientations. This suggests that observers
should reduce the DME by careful choice of target, a possibility we discuss in
some detail. |
On the radiative and thermodynamic properties of the Cosmic Microwave
Background radiation using COBE FIRAS instrument data: Use formulas to describe the monopole and dipole spectra of the Cosmic
Microwave Background (CMB) radiation, the exact expressions for the temperature
dependences of the radiative and thermodynamic functions, such as the total
radiation power per unit area, total energy density, number density of photons,
Helmholtz free energy density, entropy density, heat capacity at constant
volume, pressure, enthalpy density, and internal energy density in the finite
range of frequencies are obtained. Since the dependence of temperature upon the
redshift z is known, the obtained expressions can be simply presented in z
representation. Utilizing experimental data for the monopole and dipole spectra
measured by the COBE FIRAS instrument in the 60 - 600 GHz frequency interval at
the temperature T = 2.728 K, the values of the radiative and thermodynamic
functions, as well as the radiation density constant a and the Stefan-Boltzmann
constant are calculated. In the case of the dipole spectrum, the constants a
and the Stefan-Boltzmann constant, and the radiative and thermodynamic
properties of the CMB radiation are obtained using the mean amplitude Tamp =
3.369 m K. It is shown that the Doppler shift leads to a renormalization of the
radiation density constant a, the Stefan-Boltzmann constant, and the
corresponding constants for the thermodynamic functions. The radiative and
thermodynamic properties of the Cosmic Microwave Background radiation for the
monopole and dipole spectra at the redshift z = 1089 are calculated. | Parity violation in the CMB bispectrum by a rolling pseudoscalar: We investigate parity-violating signatures of temperature and polarization
bispectra of the cosmic microwave background (CMB) in an inflationary model
where a rolling pseudoscalar produces large equilateral tensor non-Gaussianity.
By a concrete computation based on full-sky formalism, it is shown that
resultant CMB bispectra have nonzero signals in both parity-even $(\ell_1 +
\ell_2 + \ell_3 = {\rm even})$ and parity-odd $(\ell_1 + \ell_2 + \ell_3 = {\rm
odd})$ spaces, and are almost uncorrelated with usual scalar-mode equilateral
bispectra. These characteristic signatures and polarization information help to
detect such tensor non-Gaussianity. Use of both temperature and E-mode
bispectra potentially improves of $400\%$ the detectability with respect to an
analysis with temperature bispectrum alone. Considering B-mode bispectrum, the
signal-to-noise ratio may be able to increase by 3 orders of magnitude. We
present the $1\sigma$ uncertainties of a parameter depending on a coupling
constant and a rolling condition for the pseudoscalar expected in the ${\it
Planck}$ and the proposed PRISM experiments. |
The ALPINE-ALMA [CII] survey: Survey strategy, observations and sample
properties of 118 star-forming galaxies at $4<z<6$: The ALMA-ALPINE [CII] survey is aimed at characterizing the properties of a
sample of normal star-forming galaxies (SFGs). The ALMA Large Program to
INvestigate (ALPINE) features 118 galaxies observed in the [CII]-158$\mu$m line
and far infrared (FIR) continuum emission during the period of rapid mass
assembly, right after the end of the HI reionization, at redshifts of 4<z<6. We
present the survey science goals, the observational strategy, and the sample
selection of the 118 galaxies observed with ALMA, with an average beam minor
axis of about 0.85 arcsec, or $\sim$5 kpc at the median redshift of the survey.
The properties of the sample are described, including spectroscopic redshifts
derived from the UV-rest frame, stellar masses, and star-formation rates
obtained from a spectral energy distribution (SED) fitting. The observed
properties derived from the ALMA data are presented and discussed in terms of
the overall detection rate in [CII] and FIR continuum, with the observed
signal-to-noise distribution. The sample is representative of the SFG
population in the main sequence at these redshifts. The overall detection rate
in [CII] is 64% for a signal-to-noise ratio (S/N) threshold larger than 3.5
corresponding to a 95% purity (40% detection rate for S/N>5). Based on a visual
inspection of the [CII] data cubes together with the large wealth of ancillary
data, we find a surprisingly wide range of galaxy types, including 40% that are
mergers, 20% extended and dispersion-dominated, 13% compact, and 11% rotating
discs, with the remaining 16% too faint to be classified. This diversity
indicates that a wide array of physical processes must be at work at this
epoch, first and foremost, those of galaxy mergers. This paper sets a reference
sample for the gas distribution in normal SFGs at 4<z<6. | COSMOS weak-lensing constraints on modified gravity: The observed acceleration of the universe, explained through dark energy,
could alternatively be explained through a modification of gravity that would
also induce modifications in the evolution of cosmological perturbations. We
use new weak lensing data from the COSMOS survey to test for deviations from
General Relativity. The departure from GR is parametrized in a
model-independent way that consistently parametrizes the two-point cosmic shear
amplitude and growth. Using CMB priors, we perform a likelihood analysis. We
find constraints on the amplitude of the signal that do not indicate a
deviation from General Relativity. |
Testing the assumptions of the Effective Field Theory of Large-Scale
Structure: The Effective Field Theory of Large-Scale Structure (EFTofLSS) attempts to
amend some of the shortcomings of the traditional perturbative methods used in
cosmology. It models the evolution of long-wavelength perturbations above a
cutoff scale without the need for a detailed description of the
short-wavelength ones. Short-scale physics is encoded in the coefficients of a
series of operators composed of the long-wavelength fields, and ordered in a
systematic expansion. As applied in the literature, the EFTofLSS corrects a
summary statistic (such as the power spectrum) calculated from standard
perturbation theory by matching it to $N$-body simulations or observations.
This `bottom-up' construction is remarkably successful in extending the range
of validity of perturbation theory. In this work, we compare this framework to
a `top-down' approach, which estimates the EFT coefficients from the stress
tensor of an $N$-body simulation, and propagates the corrections to the summary
statistic. We consider simple initial conditions, viz. two sinusoidal,
plane-parallel density perturbations with substantially different frequencies
and amplitudes. We find that the leading EFT correction to the power spectrum
in the top-down model is in excellent agreement with that inferred from the
bottom-up approach which, by construction, provides an exact match to the
numerical data. This result is robust to changes in the wavelength separation
between the two linear perturbations. However, in our setup, the leading EFT
coefficient does not always grow linearly with the cosmic expansion factor as
assumed in the literature based on perturbative considerations. Instead, it
decreases after orbit crossing takes place. | Galaxy clusters in local Universe simulations without density
constraints: a long uphill struggle: Galaxy clusters are excellent cosmological probes provided that their
formation and evolution within the large scale environment are precisely
understood. Therefore studies with simulated galaxy clusters have flourished.
However detailed comparisons between simulated and observed clusters and their
population - the galaxies - are complicated by the diversity of clusters and
their surrounding environment. An original way initiated by Bertschinger as
early as 1987, to legitimize the one-to-one comparison exercise down to the
details, is to produce simulations constrained to resemble the cluster under
study within its large scale environment. Subsequently several methods have
emerged to produce simulations that look like the local Universe. This paper
highlights one of these methods and its essential steps to get simulations that
not only resemble the local Large Scale Structure but also that host the local
clusters. It includes a new modeling of the radial peculiar velocity
uncertainties to remove the observed correlation between the decreases of the
simulated cluster masses and of the amount of data used as constraints with the
distance from us. This method has the particularity to use solely radial
peculiar velocities as constraints: no additional density constraints are
required to get local cluster simulacra. The new resulting simulations host
dark matter halos that match the most prominent local clusters such as Coma.
Zoom-in simulations of the latter and of a volume larger than the 30 Mpc/h
radius inner sphere become now possible to study local clusters and their
effects. Mapping the local Sunyaev-Zel'dovich and Sachs-Wolfe effects can
follow. |
The Future of Primordial Black Holes: Open Questions and Roadmap: We discuss some of the the open questions and the roadmap in the physics of
primordial black holes. Black holes are the only dark matter candidate that is
known to actually exit. Their conjectured primordial role is admittedly based
on hypothesis rather than fact, most straightforwardly as a simple extension to
the standard models of inflation, or even, in homage to quantum physics, more
controversially via a slowing-down of Hawking evaporation. Regardless of one's
stance on the theoretical basis for their existence, the possibility of
primordial black holes playing a novel role in dark matter physics and
gravitational wave astronomy opens up a rich astrophysical phenomenology that
we lay out in this brief overview. | New constraints on very light pseudoscalars: Nearly massless axion-like particles are of interest for astrophysical
observations, and some constraints on their parameter space do exist in the
literature. Here, we propose to put new constraints on these particles using
polarisation and, in particular, the polarisation differences observed between
different quasar classes. |
Angular momentum - mass relation for dark matter haloes: We study the empirical relation between an astronomical object's angular
momentum $J$ and mass $M$, $J=\beta M^\alpha$, the $J-M$ relation, using N-body
simulations. In particular, we investigate the time evolution of the $J-M$
relation to study how the initial power spectrum and cosmological model affect
this relation, and to test two popular models of its origin - mechanical
equilibrium and tidal torque theory. We find that in the $\Lambda$CDM model,
$\alpha$ starts with a value of $\sim 1.5$ at high redshift $z$, increases
monotonically, and finally reaches $5/3$ near $z=0$, whereas $\beta$ evolves
linearly with time in the beginning, reaches a maximum and decreases, and
stabilizes finally. A three-regime scheme is proposed to understand this newly
observed picture. We show that the tidal torque theory accounts for this time
evolution behaviour in the linear regime, whereas $\alpha=5/3$ comes from the
virial equilibrium of haloes. The $J-M$ relation in the linear regime contains
the information of the power spectrum and cosmological model. The $J-M$
relations for haloes in different environments and with different merging
histories are also investigated to study the effects of a halo's non-linear
evolution. An updated and more complete understanding of the $J-M$ relation is
thus obtained. | Determining $H_0$ using a model-independent method: By using type Ia supernovae (SNIa) to provide the luminosity distance (LD)
directly, which depends on the value of the Hubble constant $H_0= 100 h\; {\rm
km\; s^{-1}\; Mpc^{-1}}$, and the angular diameter distance from galaxy
clusters or baryon acoustic oscillations (BAOs) to give the derived LD
according to the distance duality relation, we propose a model-independent
method to determine $h$ from the fact that different observations should give
the same LD at a given redshift. Combining the Sloan Digital Sky Survey II
(SDSS-II) SNIa from the MLCS2k2 light curve fit and galaxy cluster data, we
find that at the $1\sigma$ confidence level (CL), $h=0.5867\pm0.0303$ for the
sample of the elliptical $\beta$ model for galaxy clusters, and
$h=0.6199\pm0.0293$ for that of the spherical $\beta$ model. The former is
smaller than the values from other observations, whereas the latter is
consistent with the Planck result at the $2\sigma$ CL and agrees very well with
the value reconstructed directly from the $H(z)$ data. With the SDSS-II SNIa
and BAO measurements, a tighter constraint, $h=0.6683\pm0.0221$, is obtained.
For comparison, we also consider the Union 2.1 SNIa from the SALT2 light curve
fitting. The results from the Union 2.1 SNIa are slightly larger than those
from the SDSS-II SNIa, and the Union 2.1 SNIa + BAOs give the tightest value.
We find that the values from SNIa + BAOs are quite consistent with those from
the Planck and the BAOs, as well as the local measurement from Cepheids and
very-low-redshift SNIa. |
CMB statistical anisotropies of classical and quantum origins: We examine the impact of different anisotropic relics on inflation, in
particular the predictions on the density perturbations. These relics can be
the source of the large scale anomalies in the cosmic microwave background.
There are two different types of background relics, one from the matter sector
and the other purely from the metric. Although the angular-dependence of the
statistical anisotropy in both cases are degenerate, the scale-dependence are
observationally distinctive. In addition, we demonstrate that non-Bunch-Davies
vacuum states can extend the statistical anisotropy to much shorter scales, and
leave a scale-dependence that is insensitive to the different backgrounds but
sensitive to the initial quantum state. | Local Luminous Infrared Galaxies: Spatially resolved mid-infrared
observations with Spitzer/IRS: Luminous Infrared (IR) Galaxies (LIRGs) are an important cosmological class
of galaxies as they are the main contributors to the co-moving star formation
rate density of the universe at z=1. In this paper we present a GTO Spitzer IRS
program aimed to obtain spectral mapping of a sample of 14 local (d<76Mpc)
LIRGs. The data cubes map, at least, the central 20arcsec x 20arcsec to
30arcsec x 30arcsec regions of the galaxies, and use all four IRS modules
covering the full 5-38micron spectral range. The final goal of this project is
to characterize fully the mid-IR properties of local LIRGs as a first step to
understanding their more distant counterparts. In this paper we present the
first results of this GTO program. The IRS spectral mapping data allow us to
build spectral maps of the bright mid-IR emission lines (e.g., [NeII], [NeIII],
[SIII], H_2), continuum, the 6.2 and 11.3micron PAH features, and the 9.7micron
silicate feature, as well as to extract 1D spectra for regions of interest in
each galaxy. The IRS data are used to obtain spatially resolved measurements of
the extinction using the 9.7micron silicate feature, and to trace star forming
regions using the neon lines and the PAH features. We also investigate a number
of AGN indicators, including the presence of high excitation emission lines and
a strong dust continuum emission at around 6micron. We finally use the
integrated Spitzer/IRS spectra as templates of local LIRGs. We discuss several
possible uses for these templates, including the calibration of the star
formation rate of IR-bright galaxies at high redshift. We also predict the
intensities of the brightest mid-IR emission lines for LIRGs as a function of
redshift, and compare them with the expected sensitivities of future space IR
missions. |
Spatial Curvature Falsifies Eternal Inflation: Inflation creates large-scale cosmological density perturbations that are
characterized by an isotropic, homogeneous, and Gaussian random distribution
about a locally flat background. Even in a flat universe, the spatial curvature
measured within one Hubble volume receives contributions from long wavelength
perturbations, and will not in general be zero. These same perturbations
determine the Cosmic Microwave Background (CMB) temperature fluctuations, which
are O(10^-5). Consequently, the low-l multipole moments in the CMB temperature
map predict the value of the measured spatial curvature \Omega_k. On this basis
we argue that a measurement of |\Omega_k| > 10^-4 would rule out slow-roll
eternal inflation in our past with high confidence, while a measurement of
\Omega_k < -10^-4 (which is positive curvature, a locally closed universe)
rules out false-vacuum eternal inflation as well, at the same confidence level.
In other words, negative curvature (a locally open universe) is consistent with
false-vacuum eternal inflation but not with slow-roll eternal inflation, and
positive curvature falsifies both. Near-future experiments will dramatically
extend the sensitivity of \Omega_k measurements and constitute a sharp test of
these predictions. | Limits on primordial magnetic fields from primordial black hole
abundance: Primordial magnetic field (PMF) is one of the feasible candidates to explain
observed large-scale magnetic fields, for example, intergalactic magnetic
fields. We present a new mechanism that brings us information about PMFs on
small scales based on the abundance of primordial black holes (PBHs). The
anisotropic stress of the PMFs can act as a source of the super-horizon
curvature perturbation in the early universe. If the amplitude of PMFs is
sufficiently large, the resultant density perturbation also has a large
amplitude, and thereby, the PBH abundance is enhanced. Since the anisotropic
stress of the PMFs is consist of the square of the magnetic fields, the
statistics of the density perturbation follows the non-Gaussian distribution.
Assuming Gaussian distributions and delta-function type power spectrum for
PMFs, based on a Monte-Carlo method, we obtain an approximate probability
density function of the density perturbation, and it is an important piece to
relate the amplitude of PMFs with the abundance of PBHs. Finally, we place the
strongest constraint on the amplitude of PMFs as a few hundred nano-Gauss on
$10^{2}\;{\rm Mpc}^{-1} \leq k\leq 10^{18}\;{\rm Mpc}^{-1}$ where the typical
cosmological observations never reach. |
A Dark Matter Superfluid: In this talk we present a novel framework that unifies the stunning success
of MOND on galactic scales with the triumph of the LambdaCDM model on
cosmological scales. This is achieved through the rich and well-studied physics
of superfluidity. The dark matter and MOND components have a common origin,
representing different phases of a single underlying substance. In galaxies,
dark matter thermalizes and condenses to form a superfluid phase. The
superfluid phonons couple to baryonic matter particles and mediate a MOND-like
force. Our framework naturally distinguishes between galaxies (where MOND is
successful) and galaxy clusters (where MOND is not): dark matter has a higher
temperature in clusters, and hence is in a mixture of superfluid and normal
phase. The rich and well-studied physics of superfluidity leads to a number of
striking observational signatures, which we briefly discuss. Remarkably the
critical temperature and equation of state of the dark matter superfluid are
similar to those of known cold atom systems. Identifying a precise cold atom
analogue would give important insights on the microphysical interactions
underlying DM superfluidity. Tantalizingly, it might open the possibility of
simulating the properties and dynamics of galaxies in laboratory experiments. | Direct detection of WIMPs : Implications of a self-consistent truncated
isothermal model of the Milky Way's dark matter halo: Direct detection of Weakly Interacting Massive Particle (WIMP) candidates of
Dark Matter (DM) is studied within the context of a self-consistent truncated
isothermal model of the finite-size dark halo of the Galaxy based on the "King
model" of the phase space distribution function of collisionless DM particles.
Our halo model takes into account the modifications of the phase-space
structure of the halo due to the gravitational influence of the observed
visible matter in a self-consistent manner. The parameters of the halo model
are determined by a fit to a recently determined circular rotation curve of the
Galaxy that extends up to $\sim$ 60 kpc. Unlike in the Standard Halo Model
(SHM) customarily used in the analysis of the results of WIMP direct detection
experiments, the velocity distribution of the WIMPs in our model is
non-Maxwellian with a cut-off at a maximum velocity that is self-consistently
determined by the model itself. For our halo model that provides the best fit
to the rotation curve data, the 90% C.L. upper limit on the WIMP-nucleon
spin-independent cross section from the recent results of the CDMS-II
experiment, for example, is $\sim 5.3\times10^{-8}\pb$ at a WIMP mass of $\sim$
71 GeV. We also find, using the original 2-bin annual modulation amplitude data
of the DAMA experiment, that there exists a range of small WIMP masses,
typically $\sim$ 2 -- 16 GeV, within which DAMA collaboration's claimed annual
modulation signal purportedly due to WIMPs is compatible with the null results
of other experiments. These results strengthen the possibility of low-mass
($\lsim 10\gev$) WIMPs as a candidate for dark matter as indicated by several
earlier studies performed within the context of the SHM. A more rigorous
analysis using DAMA bins over smaller intervals should be able to better
constrain the "DAMA regions" in the WIMP parameter space within the context of
our model. |
The Balmer decrement of SDSS galaxies: High resolution spectra are necessary to distinguish and correctly measure
the Balmer emission lines due to the presence of strong metal and Balmer
absorption features in the stellar continuum. This accurate measurement is
necessary for use in emission line diagnostics, such as the Balmer decrement
(i.e. Halpha/Hbeta), used to determine the attenuation of galaxies. Yet at high
redshifts obtaining such spectra becomes costly. Balmer emission line
equivalent widths are much easier to measure, requiring only low resolution
spectra or even simple narrow band filters and therefore shorter observation
times. However a correction for the stellar continuum is still needed for this
equivalent width Balmer decrement. We present here a statistical analysis of
the Sloan Digital Sky Survey Data Release 7 emission line galaxy sample, using
the spectrally determined Balmer emission line fluxes and equivalent widths.
Using the large numbers of galaxies available in the SDSS catalogue, we
determined an equivalent width Balmer decrement including a statistically-based
correction for the stellar continuum. Based on this formula, the attenuation of
galaxies can now be obtained from low spectral resolution observations. In
addition, this investigation also revealed an error in the Hbeta line fluxes,
within the SDSS DR7 MPA/JHU catalogue, with the equivalent widths
underestimated by average ~0.35A in the emission line galaxy sample. This error
means that Balmer decrement determined attenuations are overestimated by a
systematic 0.1 magnitudes in A_V, and future analyses of this sample need to
include this correction. | Testing spherical evolution for modelling void abundances: We compare analytical predictions of void volume functions to those measured
from N-body simulations, detecting voids with the zobov void finder. We push to
very small, nonlinear voids, below few Mpc radius, by considering the unsampled
DM density field. We also study the case where voids are identified using
halos. We develop analytical formula for the void abundance of both the
excursion set approach and the peaks formalism. These formula are valid for
random walks smoothed with a top-hat filter in real space, with a large class
of realistic barrier models. We test the extent to which the spherical
evolution approximation, which forms the basis of the analytical predictions,
models the highly aspherical voids that occur in the cosmic web, and are found
by a watershed-based algorithm such as zobov. We show that the volume function
returned by zobov is quite sensitive to the choice of treatment of sub-voids, a
fact that has not been appreciated previously. For reasonable choices of
sub-void exclusion, we find that the Lagrangian density delta_v of the zobov
voids -- which is predicted to be a constant delta_v = -2.7 in the spherical
evolution model -- is different from the predicted value, showing substantial
scatter and scale dependence. This result applies to voids identified at z=0
with effective radius between 1 and 10 Mpc/h. Our analytical approximations are
flexible enough to give a good description of the resulting volume function;
however, this happens for choices of parameter values that are different from
those suggested by the spherical evolution assumption. We conclude that
analytical models for voids must move away from the spherical approximation in
order to be applied successfully to observations, and we discuss some possible
ways forward. |
From galactic bars to the Hubble tension: weighing up the astrophysical
evidence for Milgromian gravity: Astronomical observations reveal a major deficiency in our understanding of
physics $-$ the detectable mass is insufficient to explain the observed motions
in a huge variety of systems given our current understanding of gravity,
Einstein's General theory of Relativity (GR). This missing gravity problem may
indicate a breakdown of GR at low accelerations, as postulated by Milgromian
dynamics (MOND). We review the MOND theory and its consequences, including in a
cosmological context where we advocate a hybrid approach involving light
sterile neutrinos to address MOND's cluster-scale issues. We then test the
novel predictions of MOND using evidence from galaxies, galaxy groups, galaxy
clusters, and the large-scale structure of the Universe. We also consider
whether the standard cosmological paradigm ($\Lambda$CDM) can explain the
observations and review several previously published highly significant
falsifications of it. Our overall assessment considers both the extent to which
the data agree with each theory and how much flexibility each has when
accommodating the data, with the gold standard being a clear $a~priori$
prediction not informed by the data in question. Our conclusion is that MOND is
favoured by a wealth of data across a huge range of astrophysical scales,
ranging from the kpc scales of galactic bars to the Gpc scale of the local
supervoid and the Hubble tension, which is alleviated in MOND through enhanced
cosmic variance. We also consider several future tests, mostly on scales much
smaller than galaxies. | The evolution of clustering length, large-scale bias and host halo mass
at 2<z<5 in the VIMOS Ultra Deep Survey (VUDS): We investigate the evolution of galaxy clustering for galaxies in the
redshift range 2.0<$z$<5.0 using the VIMOS Ultra Deep Survey (VUDS). We present
the projected (real-space) two-point correlation function $w_p(r_p)$ measured
by using 3022 galaxies with robust spectroscopic redshifts in two independent
fields (COSMOS and VVDS-02h) covering in total 0.8 deg$^2$. We quantify how the
scale dependent clustering amplitude $r_0$ changes with redshift making use of
mock samples to evaluate and correct the survey selection function. Using a
power-law model $\xi(r) = (r/r_0)^{-\gamma}$ we find that the correlation
function for the general population is best fit by a model with a clustering
length $r_0$=3.95$^{+0.48}_{-0.54}$ h$^{-1}$Mpc and slope
$\gamma$=1.8$^{+0.02}_{-0.06}$ at $z$~2.5, $r_0$=4.35$\pm$0.60 h$^{-1}$Mpc and
$\gamma$=1.6$^{+0.12}_{-0.13}$ at $z$~3.5. We use these clustering parameters
to derive the large-scale linear galaxy bias $b_L^{PL}$, between galaxies and
dark matter. We find $b_L^{PL}$ = 2.68$\pm$0.22 at redshift $z$~3 (assuming
$\sigma_8$ = 0.8), significantly higher than found at intermediate and low
redshifts. We fit an HOD model to the data and we obtain that the average halo
mass at redshift $z$~3 is $M_h$=10$^{11.75\pm0.23}$ h$^{-1}$M$_{\odot}$. From
this fit we confirm that the large-scale linear galaxy bias is relatively high
at $b_L^{HOD}$ = 2.82$\pm$0.27. Comparing these measurements with similar
measurements at lower redshifts we infer that the star-forming population of
galaxies at $z$~3 should evolve into the massive and bright ($M_r$<-21.5)
galaxy population which typically occupy haloes of mass $\langle M_h\rangle$ =
10$^{13.9}$ h$^{-1}$ $M_{\odot}$ at redshift $z$=0. |
Ly alpha escape during cosmological hydrogen recombination: the 3d-1s
and 3s-1s two-photon processes: We give a formulation of the radiative transfer equation for Lyman alpha
photons which allows us to include the two-photon corrections for the 3s-1s and
3d-1s decay channels during cosmological hydrogen recombination. We use this
equation to compute the corrections to the Sobolev escape probability for Lyman
alpha photons during hydrogen recombination, which then allow us to calculate
the changes in the free electron fraction and CMB temperature and polarization
power spectra. We show that the effective escape probability changes by DP/P ~+
11% at z~1400 in comparison with the one obtained using the Sobolev
approximation. This speeds up of hydrogen recombination by DN_e/N_e ~- 1.6% at
z~1190, implying |DC_l/C_l| ~1%-3% at l >~ 1500 with shifts in the positions of
the maxima and minima in the CMB power spectra. These corrections will be
important for the analysis of future CMB data.
The total correction is the result of the superposition of three independent
processes, related to (i) time-dependent aspects of the problem, (ii)
corrections due to quantum mechanical deviations in the shape of the emission
and absorption profiles in the vicinity of the Lyman alpha line from the normal
Lorentzian, and (iii) a thermodynamic correction factor, which occurs to be
very important. All these corrections are neglected in the
Sobolev-approximation, but they are important in the context of future CMB
observations. All three can be naturally obtained in the two-photon formulation
of the Lyman alpha absorption process. However, the corrections (i) and (iii)
can also be deduced in the normal '1+1' photon language, without necessarily
going to the two-photon picture. Therefore only (ii) is really related to the
quantum mechanical aspects of the two-photon process (abridged) | Statistical effects of the observer's peculiar velocity on source number
counts: The velocity of the Sun with respect to the cosmic microwave background (CMB)
can be extracted from the CMB dipole, provided its intrinsic dipole is assumed
to be small in comparison. This interpretation is consistent, within fairly
large error bars, with the measurement of the correlations between neighboring
CMB multipoles induced by the velocity of the observer, which effectively
breaks isotropy. In contrast, the source number count dipole was reported to
privilege a velocity of the observer with an amplitude which is about twice as
large as the one extracted from the entirely kinematic interpretation of the
CMB dipole, with error bars which indicate a more and more significant tension.
In this work, we study the effect of the peculiar velocity of the observer on
correlations of nearby multipoles in the source number counts. We provide an
unbiased estimator for the kinetic dipole amplitude, which is proportional to
the peculiar velocity of the observer and we compute the expected signal to
noise ratio. Near future experiments can achieve better than 5$\%$ constraints
on the velocity of the Sun with our estimator. |
On the Radio and Optical Luminosity Evolution of Quasars: We calculate simultaneously the radio and optical luminosity evolutions of
quasars, and the distribution in radio loudness R defined as the ratio of radio
and optical luminosities, using a flux limited data set containing 636 quasars
with radio and optical fluxes from White et al. We first note that when dealing
with multivariate data it is imperative to first determine the true
correlations among the variables, not those introduced by the observational
selection effects, before obtaining the individual distributions of the
variables. We use the methods developed by Efron and Petrosian which are
designed to obtain unbiased correlations, distributions, and evolution with
redshift from a data set truncated due to observational biases. It is found
that the population of quasars exhibits strong positive correlation between the
radio and optical luminosities. With this correlation, whether intrinsic or
observationally induced accounted for, we find that there is a strong
luminosity evolution with redshift in both wavebands, with significantly higher
radio than optical evolution. We also construct the local radio and optical
luminosity functions and the density evolution. Finally, we consider the
distribution of the radio loudness parameter R obtained from careful treatment
of the selection effects and luminosity evolutions with that obtained from the
raw data without such considerations. We find a significant difference between
the two distributions and no clear sign of bi-modality in the true distribution
for the range of R values considered. Our results indicate therefore, somewhat
surprisingly, that there is no critical switch in the efficiency of the
production of disk outflows/jets between very radio quiet and very radio loud
quasars, but rather a smooth transition. Also, this efficiency seems higher for
the high-redshift and more luminous sources in the considered sample. | Disentangling the gamma-ray emission of NGC1275 and that of the Perseus
cluster: (Abridged). The gamma-ray emission from galaxy clusters hosting active
galaxies is a complex combination of diffuse and point-like emission with
different spectral and spatial properties. We discuss the case of the Perseus
cluster containing the radio-galaxy NGC 1275 that has been detected as a bright
gamma-ray source by the Fermi-LAT experiment. We provide a detailed study of
the gamma-ray emission coming from the core of Perseus by modeling the central
AGN emission with a multiple plasma blob model, and the emission from the
cluster atmosphere with both a Warming Ray (WR) model and Dark Matter (DM)
neutralino annihilation models. We set constraints on both the central galaxy
and cluster SED models by using multi-frequency data including the observations
obtained by Fermi and MAGIC. We find that: i) in all the viable models for the
cluster gamma-ray emission, the emission detected by Fermi from the Perseus
core is dominated by the active galaxy NGC 1275, that is found in a
high-emission state; ii) the diffuse gamma-ray emission of the cluster, in the
WR model and in the DM models with the highest allowed normalization, could be
detected by Fermi if the central emission from NGC1275 is in a low-emission
state; iii) Fermi can have the possibility to resolve and detect the diffuse
gamma-ray flux coming from the outer corona of the Perseus atmosphere at r> 800
kpc. Our results show that a simultaneous study of the various emission
mechanisms that produce diffuse gamma-rays from galaxy clusters and those
producing gamma-rays from active galaxies residing in the cluster atmospheres
is crucial first to disentangle the spectral and spatial characteristics of the
gamma-ray emission and secondly to assess the optimal observational strategy in
the attempt to reveal the still elusive diffuse gamma-ray emission widely
predicted for the atmospheres of large-scale structures. |
Precision Tests of CO and [CII] Power Spectra Models against Simulated
Intensity Maps: Line intensity mapping (LIM) is an emerging technique with a unique potential
to probe a wide range of scales and redshifts. Realizing the full potential of
LIM, however, relies on accurate modeling of the signal. We introduce an
extended halo model for the power spectrum of intensity fluctuations of CO
rotational lines and [CII] fine transition line in real space, modeling
nonlinearities in matter fluctuations and biasing relation between the line
intensity fluctuations and the underlying dark matter distribution. We also
compute the stochastic contributions beyond the Poisson approximation using the
halo model framework. To establish the accuracy of the model, we create the
first cosmological-scale simulations of CO and [CII] intensity maps,
\textsf{MithraLIMSims}, at redshifts $0.5 \leq z\leq6$, using halo catalogs
from Hidden-Valley simulations, and painting halos according to
mass-redshift-luminosity relations for each line. We show that at $z=1$ on
scales $k_{\rm max} \lesssim 0.8 \ {\rm Mpc}^{-1}h$, the model predictions of
clustering power (with only two free parameters) are in agreement with the
measured power spectrum at better than 5\%. At higher redshift of $z=4.5$, this
remarkable agreement extends to smaller scale of $ k_{\rm max} \lesssim 2 \
{\rm Mpc}^{-1}h$. Furthermore, we show that on large scales, the stochastic
contributions to CO and CII power spectra are non-Poissonian, with amplitudes
reproduced reasonably well by the halo model prescription. Lastly, we assess
the performance of the theoretical model of the baryon acoustic oscillations
(BAO) and show that hypothetical LIM surveys probing CO lines at $z=1$, that
can be deployed within this decade, will be able to make a high significance
measurement of the BAO. On a longer time scale, a space-based mission probing
[CII] line can uniquely measure the BAO on a wide range of redshifts at an
unprecedented precision. | Constraining the role of star cluster mergers in nuclear cluster
formation: Simulations confront integral-field data: We present observations and dynamical models of the stellar nuclear clusters
(NCs) at the centres of NGC 4244 and M33. We then compare these to an extensive
set of simulations testing the importance of purely stellar dynamical mergers
on the formation and growth of NCs. Mergers of star clusters are able to
produce a wide variety of observed properties, including densities, structural
scaling relations, shapes (including the presence of young discs) and even
rapid rotation. Nonetheless, difficulties remain, most notably that the second
order kinematic moment V_rms = (V^2 + sigma^2)^(1/2) of the models is too
centrally peaked to match observations. This can be remedied by the merger of
star clusters onto a pre-existing nuclear disc, but the line-of-sight velocity
V is still more slowly rising than in NGC 4244. Our results therefore suggest
that purely stellar dynamical mergers cannot form NCs, and that gas dissipation
is a necessary ingredient for at least ~50% of a NC's mass. The negative
vertical anisotropy found in NGC 4244 however requires at least 10% of the mass
to be accreted as stars, since gas dissipation and in situ star formation leads
to positive vertical anisotropy. |
Carbon Detection in Early-Time Optical Spectra of Type Ia Supernovae: While O is often seen in spectra of Type Ia supernovae (SNe Ia) as both
unburned fuel and a product of C burning, C is only occasionally seen at the
earliest times, and it represents the most direct way of investigating
primordial white dwarf material and its relation to SN Ia explosion scenarios
and mechanisms. In this paper, we search for C absorption features in 188
optical spectra of 144 low-redshift (z < 0.1) SNe Ia with ages <3.6 d after
maximum brightness. These data were obtained as part of the Berkeley SN Ia
Program (BSNIP; Silverman et al. 2012) and represent the largest set of SNe Ia
in which C has ever been searched. We find that ~11 per cent of the SNe studied
show definite C absorption features while ~25 per cent show some evidence for C
II in their spectra. Also, if one obtains a spectrum at t < -5 d, then there is
a better than 30 per cent chance of detecting a distinct absorption feature
from C II. SNe Ia that show C are found to resemble those without C in many
respects, but objects with C tend to have bluer optical colours than those
without C. The typical expansion velocity of the C II {\lambda}6580 feature is
measured to be 12,000-13,000 km/s, and the ratio of the C II {\lambda}6580 to
Si II {\lambda}6355 velocities is remarkably constant with time and among
different objects with a median value of ~1.05. While the pseudo-equivalent
widths (pEWs) of the C II {\lambda}6580 and C II {\lambda}7234 features are
found mostly to decrease with time, we see evidence of a significant increase
in pEW between ~12 and 11 d before maximum brightness, which is actually
predicted by some theoretical models. The range of pEWs measured from the BSNIP
data implies a range of C mass in SN Ia ejecta of about (2-30) * 10^-3 M_Sun. | Pulsar Timing Array Constraints on Primordial Black Holes with NANOGrav
11-Year Data Set: The detection of binary black hole coalescences by LIGO/Virgo has aroused the
interest in primordial black holes (PBHs), because they could be both the
progenitors of these black holes and a compelling candidate of dark matter
(DM). PBHs are formed soon after the enhanced scalar perturbations re-enter
horizon during radiation dominated era, which would inevitably induce
gravitational waves as well. Searching for such scalar induced gravitational
waves (SIGWs) provides an elegant way to probe PBHs. We perform the first
direct search for the signals of SIGWs accompanying the formation of PBHs in
North American Nanohertz Observatory for Gravitational waves (NANOGrav) 11-year
data set. No statistically significant detection has been made, and hence we
place a stringent upper limit on the abundance of PBHs at $95\%$ confidence
level. In particular, less than one part in a million of the total DM mass
could come from PBHs in the mass range of $[2 \times 10^{-3}, 7\times 10^{-1}]
\Msun$. |
Toward unbiased estimations of the statefinder parameters: With the use of simulated supernova catalogs, we show that the statefinder
parameters turn out to be poorly and biased estimated by standard cosmography.
To this end, we compute their standard deviations and several bias statistics
on cosmologies near the concordance model, demonstrating that these are very
large, making standard cosmography unsuitable for future and wider compilations
of data. To overcome this issue, we propose a new method that consists in
introducing the series of the Hubble function into the luminosity distance,
instead of considering the usual direct Taylor expansions of the luminosity
distance. Moreover, in order to speed up the numerical computations, we
estimate the coefficients of our expansions in a hierarchical manner, in which
the order of the expansion depends on the redshift of every single piece of
data. In addition, we propose two hybrids methods that incorporates standard
cosmography at low redshifts. The methods presented here perform better than
the standard approach of cosmography both in the errors and bias of the
estimated statefinders. We further propose a one-parameter diagnostic to reject
non-viable methods in cosmography. | Testing for a large local void by investigating the Near-Infrared Galaxy
Luminosity Function: Recent cosmological modeling efforts have shown that a local underdensity on
scales of a few hundred Mpc (out to z ~ 0.1), could produce the apparent
acceleration of the expansion of the universe observed via type Ia supernovae.
Several studies of galaxy counts in the near-infrared (NIR) have found that the
local universe appears under-dense by ~25-50% compared with regions a few
hundred Mpc distant. Galaxy counts at low redshifts sample primarily L ~ L*
galaxies. Thus, if the local universe is under-dense, then the normalization of
the NIR galaxy luminosity function (LF) at z>0.1 should be higher than that
measured for z<0.1. Here we present a highly complete (> 90%) spectroscopic
sample of 1436 galaxies selected in the H-band to study the normalization of
the NIR LF at 0.1<z<0.3 and address the question of whether or not we reside in
a large local underdensity. We find that for the combination of our six fields,
the product phi* L* at 0.1 < z < 0.3 is ~ 30% higher than that measured at
lower redshifts. While our statistical errors in this measurement are on the
~10% level, we find the systematics due to cosmic variance may be larger still.
We investigate the effects of cosmic variance on our measurement using the
COSMOS cone mock catalogs from the Millennium simulation and recent empirical
estimates. We find that our survey is subject to systematic uncertainties due
to cosmic variance at the 15% level ($1 sigma), representing an improvement by
a factor of ~ 2 over previous studies in this redshift range. We conclude that
observations cannot yet rule out the possibility that the local universe is
under-dense at z<0.1. |
X-raying the Winds of Luminous Active Galaxies: We briefly describe some recent observational results, mainly at X-ray
wavelengths, on the winds of luminous active galactic nuclei (AGNs). These
winds likely play a significant role in galaxy feedback. Topics covered include
(1) Relations between X-ray and UV absorption in Broad Absorption Line (BAL)
and mini-BAL quasars; (2) X-ray absorption in radio-loud BAL quasars; and (3)
Evidence for relativistic iron K BALs in the X-ray spectra of a few bright
quasars. We also mention some key outstanding problems and prospects for future
advances; e.g., with the International X-ray Observatory (IXO). | On the relation between Seyfert 2 accretion rate and environment at z <
0.1: We analyse different properties of the small scale environment of Seyfert 2
for two samples selected according to the accretion rate parameter, R, from the
DR7-SDSS survey. We compare the results with two control samples of non-active
galaxies that cover the same redshift range, luminosity, colours, morphology,
age and stellar mass content. Our study shows that both high and low accretion
rate subsamples reside in bluer and lower density environments than the control
samples. However, we find that this difference is at least two times stronger
for the low accretion rate Seyferts.
In the vicinity of Seyfert 2, red galaxies have systematically lower values
of stellar-mass as compared with corresponding control samples. The lower
values of stellar mass for red neighbours is more significant at higher density
environments and it is more evident for low accretion rate Seyfert. We also
find that this effect is independent of the host's stellar mass.
Our results are consistent with a scenario where AGN occurrence is higher in
lower/medium density environments with a higher merger rate and a lack of a
dense intergalactic medium (that can strip gas from these systems) that provide
suitable conditions for the central black hole feeding. We find this
particularly evident for the low accretion rate Seyferts that could compensate
through the intergalactic medium the lack of gas of their hosts. |
The Araucaria Project. Determination of the LMC Distance from Late-Type
Eclipsing Binary Systems: I. OGLE-051019.64-685812.3: We have analyzed the double-lined eclipsing binary system
OGLE-051019.64-685812.3 in the LMC which consists of two G4 giant components
with very similar effective temperatures. A detailed analysis of the OGLE
I-band light curve of the system, radial velocity curves for both components
derived from high-resolution spectra, and near-infrared magnitudes of the
binary system measured outside the eclipses has allowed us to obtain an
accurate orbit solution for this eclipsing binary, and its fundamental physical
parameters. Using a surface brightness-(V-K) color relation for giant stars we
have calculated the distance to the system and obtain a true distance modulus
of 18.50 mag, with an estimated total uncertainty of ~ 3 %. More similar
eclipsing binary systems in the LMC which we have discovered and for which we
are currently obtaining the relevant data will allow us to better check on the
systematics of the method and eventually provide a distance determination to
the LMC accurate to 1 percent, so much needed for the calibration of the
distance scale. | The metal-enriched host of an energetic gamma-ray burst at z ~ 1.6: (Abridged) Long gamma-ray burst (GRB) host galaxies might open a short-cut to
the characteristics of typical star-forming galaxies throughout the history of
the Universe. Due to the absence of near-infrared (NIR) spectroscopy, however,
detailed investigations, specifically a determination of the gas-phase
metallicity of gamma-ray burst hosts, was largely limited to redshifts z < 1 to
date. Here, we report observations of the galaxy hosting GRB 080605 at z = 1.64
using optical/NIR spectroscopy and high-resolution HST/WFC3 imaging. We avail
of VLT/X-shooter spectroscopy to measure the metallicity, electron density,
star-formation rate (SFR), and reddening of the host. Specifically, we use
different strong-line diagnostics based on [N II] to robustly measure the
gas-phase metallicity for the first time for a GRB host at this redshift. The
host of the energetic (E_iso ~ 2 x 10^53 erg) GRB 080605 is a morphologically
complex, vigorously star-forming galaxy with an H\alpha-derived SFR of 31
M_sun/yr. Its ISM is significantly enriched with metals with an oxygen
abundance between 8.3 and 8.6 depending on the adopted strong-line calibrator.
This corresponds to values in the range of 0.4-0.8 times the solar value. For
its measured stellar mass of 8 x 10^9 M_sun and SFR this value is consistent
with the fundamental metallicity relation defined by star-forming field
galaxies. Our observations directly illustrate that GRB hosts are not
necessarily metal-poor, both on absolute scales as well as relative to their
stellar mass and SFR. GRB hosts could thus be fair tracers of the population of
ordinary star-forming galaxies as a whole at high redshift. |
Validating estimates of the growth rate of structure with modified
gravity simulations: We perform a validation of estimates of the growth rate of structure,
described by the parameter combination $f\sigma_8$, in modified gravity
cosmologies. We consider an analysis pipeline based on the redshift-space
distortion modelling of the clustering wedges statistic of the galaxy
correlation function and apply it to mock catalogues of $\Lambda{\rm CDM}$ and
the normal branch of DGP cosmologies. We employ a halo occupation distribution
approach to construct our mocks, which we ensure resemble the CMASS sample from
BOSS in terms of the total galaxy number density and large scale amplitude of
the power spectrum monopole. We show that the clustering wedges model
successfully recovers the true growth rate difference between DGP and
$\Lambda{\rm CDM}$, even for cases with over 40\% enhancement in $f\sigma_8$
compared to $\Lambda{\rm CDM}$. The unbiased performance of the clustering
wedges model allows us to use the growth rate values estimated from the BOSS
DR12 data to constrain the cross-over scale $r_c$ of DGP gravity to
$\left[r_cH_0\right]^{-1} < 0.97$ ($2\sigma$) or $r_c > 3090\ {\rm Mpc}/h$,
cutting into the interesting region of parameter space with $r_c \sim H_0^{-1}$
using constraints from the growth of structure alone. | Hubble Space Telescope Observations of Mira Variables in the Type Ia
Supernova Host NGC 1559: An Alternative Candle to Measure the Hubble Constant: We present year-long, near-infrared Hubble Space Telescope WFC3 observations
used to search for Mira variables in NGC 1559, the host galaxy of the Type Ia
supernova (SN Ia) 2005df. This is the first dedicated search for Miras,
highly-evolved low-mass stars, in a SN Ia host and subsequently the first
calibration of the SN Ia luminosity using Miras in a role historically played
by Cepheids. We identify a sample of 115 O-rich Miras with P < 400 days based
on their light curve properties. We find that the scatter in the Mira
Period-Luminosity Relation (PLR) is comparable to Cepheid PLRs seen in SN Ia
supernova host galaxies. Using a sample of O-rich Miras discovered in NGC 4258
with HST F160W and its maser distance, we measure a distance modulus for NGC
1559 of mu1559 = 31.41 +/- 0.050 (statistical) +/- 0.060 (systematic) mag.
Based on the light curve of the normal, well-observed, low-reddening SN 2005df,
we obtain a measurement of the fiducial SN Ia absolute magnitude of MB0 =
-19.27 +/- 0.13 mag. With the Hubble diagram of SNe Ia we find H0 = 72.7 +/-
4.6 kms-1 Mpc-1. Combining the calibration from the NGC 4258 megamaser and the
Large Magellanic Cloud detached eclipsing binaries gives a best value of H0 =
73.3 +/- 4.0 km s-1 Mpc-1. This result is within 1-sigma of the Hubble constant
derived using Cepheids and multiple calibrating SNe Ia. This is the first of
four expected calibrations of the SN Ia luminosity from Miras which should
reduce the error in H0 via Miras to ~3%. In light of the present Hubble tension
and JWST, Miras have utility in the extragalactic distance scale to check
Cepheid distances or calibrate nearby SNe in early-type host galaxies that
would be unlikely targets for Cepheid searches. |
The Herschel Stripe 82 Survey (HerS): Maps and Early Catalog: We present the first set of maps and band-merged catalog from the Herschel
Stripe 82 Survey (HerS). Observations at 250, 350, and 500 micron were taken
with the Spectral and Photometric Imaging Receiver (SPIRE) instrument aboard
the Herschel Space Observatory. HerS covers 79 deg$^2$ along the SDSS Stripe 82
to a depth of 13.0, 12.9, and 14.8 mJy beam$^{-1}$ (including confusion) at
250, 350, and 500 micron, respectively. HerS was designed to measure
correlations with external tracers of the dark matter density field --- either
point-like (i.e., galaxies selected from radio to X-ray) or extended (i.e.,
clusters and gravitational lensing) --- in order to measure the bias and
redshift distribution of intensities of infrared-emitting dusty star-forming
galaxies and AGN. By locating HeRS in Stripe 82, we maximize the overlap with
available and upcoming cosmological surveys. The band-merged catalog contains
3.3x10$^4$ sources detected at a significance of >3 $\sigma$ (including
confusion noise). The maps and catalog are available at
http://www.astro.caltech.edu/hers/ | Scattered Emission from z~1 Galactic Outflows: Mapping Mg II resonance emission scattered by galactic winds offers a means
to determine the spatial extent and density of the warm outflow. Using
Keck/LRIS spectroscopy, we have resolved scattered Mg II emission to the east
of 32016857, a star-forming galaxy at z =0.9392 with an outflow. The Mg II
emission from this galaxy exhibits a P-Cygni profile, extends further than both
the continuum and [O II] emission along the eastern side of the slit, and has a
constant Doppler shift along the slit which does not follow the velocity
gradient of the nebular [O II] emission. Using the Sobolev approximation, we
derive the density of Mg+ ions at a radius of 12 to 18 kpc in the outflow. We
model the ionization correction and find that much of the outflowing Mg is in
Mg++. We estimate that the total mass flux could be as large as 330 - 500 solar
masses per year, with the largest uncertainties coming from the depletion of Mg
onto grains and the clumpiness of the warm outflow. We show that confining the
warm clouds with a hot wind reduces the estimated mass flux of the warm outflow
and indicates amass-loading factor near unity in the warm phase alone. Based on
the high blue luminosities that distinguish 32016857 and TKRS 4389, described
by Rubin et al. 2011, from other galaxies with P-Cygni emission, we suggest
that, as sensitivity to diffuse emission improves, scattering halos may prove
to be a generic property of star-forming galaxies at intermediate redshifts. |
Unscreening Modified Gravity in the Matter Power Spectrum: Viable modifications of gravity that may produce cosmic acceleration need to
be screened in high-density regions such as the Solar System, where general
relativity is well tested. Screening mechanisms also prevent strong anomalies
in the large-scale structure and limit the constraints that can be inferred on
these gravity models from cosmology. We find that by suppressing the
contribution of the screened high-density regions in the matter power spectrum,
allowing a greater contribution of unscreened low densities, modified gravity
models can be more readily discriminated from the concordance cosmology.
Moreover, by variation of density thresholds, degeneracies with other effects
may be dealt with more adequately. Specializing to chameleon gravity as a
worked example for screening in modified gravity, employing N-body simulations
of f(R) models and the halo model of chameleon theories, we demonstrate the
effectiveness of this method. We find that a percent-level measurement of the
clipped power at k < 0.3 h/Mpc can yield constraints on chameleon models that
are more stringent than what is inferred from Solar System tests or distance
indicators in unscreened dwarf galaxies. Finally, we verify that our method is
also applicable to the Vainshtein mechanism. | The extended ROSAT-ESO Flux-Limited X-ray Galaxy Cluster Survey (REFLEX
II) V. Exploring a local underdensity in the Southern Sky: Several claims have been made that we are located in a locally underdense
region of the Universe based on observations of supernovae and galaxy density
distributions. Two recent studies of K-band galaxy surveys have provided new
support for a local underdensity in the galaxy distribution out to distances of
200 - 300 Mpc. If confirmed, such large local underdensities would have
important implications on the interpretation of local measurements of
cosmological parameters. Galaxy clusters have been shown to be ideal probes to
trace the large-scale structure of the Universe. In this paper we study the
local density distribution in the southern sky with the X-ray detected galaxy
clusters from the REFLEX II cluster survey. From the normalized comoving number
density of clusters we find an average underdensity of ~30 - 40% in the
redshift range out to z ~0.04 (~170 Mpc) in the southern extragalactic sky with
a significance larger than 3.4sigma. On larger scales from 300 Mpc to over 1
Gpc the density distribution appears remarkably homogeneous. The local
underdensity seems to be dominated by the South Galactic Cap region. A
comparison of the cluster distribution with that of galaxies in the K-band from
a recent study shows that galaxies and clusters trace each other very closely
in density. In the South Galactic Cap region both surveys find a local
underdensity in the redshift range z= 0 to 0.05 and no significant underdensity
in the North Galactic Cap at southern latitudes. Our results to not support
cosmological models that attempt to interpret the cosmic acceleration by a
large local void, since the local underdensity we find is not isotropic and
limited to a size significantly smaller than 300 Mpc radius. |
Time-Delay Cosmography: Measuring the Hubble Constant and other
cosmological parameters with strong gravitational lensing: Multiply lensed sources experience a relative time delay in the arrival of
photons. This effect can be used to measure absolute distances and the Hubble
constant ($H_0$) and is known as time-delay cosmography. The methodology is
independent of the local distance ladder and early-universe physics and
provides a precise and competitive measurement of $H_0$. With upcoming
observatories, time-delay cosmography can provide a 1% precision measurement of
$H_0$ and can decisively shed light on the current reported 'Hubble tension'.
This paper presents the theoretical background and the current techniques
applied for time-delay cosmographic studies and the measurement of the Hubble
constant. The paper describes the challenges and systematics in the different
components of the analysis and strategies to mitigate them. The current
measurements are discussed in context and the opportunities with the
anticipated data sets in the future are laid out. | How cold is Dark Matter? Constraints from Milky Way Satellites: We test the luminosity function of Milky Way satellites as a constraint for
the nature of Dark Matter particles. We perform dissipationless high-resolution
N-body simulations of the evolution of Galaxy-sized halo in the standard Cold
Dark Matter (CDM) model and in four Warm Dark Matter (WDM) scenarios, with a
different choice for the WDM particle mass (m_w). We then combine the results
of the numerical simulations with semi-analytic models for galaxy formation, to
infer the properties of the satellite population. Quite surprisingly we find
that even WDM models with relatively low m_w values (2-5 keV) are able to
reproduce the observed abundance of ultra faint (Mv<-9) dwarf galaxies, as well
as the observed relation between Luminosity and mass within 300 pc. Our results
suggest a lower limit of 1 keV for thermal warm dark matter, in broad agreement
with previous results from other astrophysical observations like Lyman-alpha
forest and gravitational lensing. |
ALFALFA HI Data Stacking II. HI content of the host galaxies of AGN: We use a stacking technique to measure the average HI content of a
volume-limited sample of 1871 AGN host galaxies from a parent sample of
galaxies selected from the SDSS and GALEX imaging surveys with stellar masses
greater than 10^10 M_sun and redshifts in the range 0.025<z<0.05. HI data are
available from the Arecibo Legacy Fast ALFA (ALFALFA) survey. In previous work,
we found that the HI gas fraction in galaxies correlates most strongly with the
combination of optical/UV colour and stellar surface mass density. We therefore
build a control sample of non-AGN matched to the AGN hosts in these two
properties. We study trends in HI gas mass fraction (M(HI)/M_*), where M_* is
the stellar mass) as a function of black hole accretion rate indicator
L[OIII]/M(BH). We find no significant difference in HI content between AGN and
control samples at all values of black hole accretion rate probed by the
galaxies in our sample. This indicates that AGN do not influence the
large-scale gaseous properties of galaxies in the local Universe. We have
studied the variation in HI mass fraction with black hole accretion rate in the
blue and red galaxy populations. In the blue population, the HI gas fraction is
independent of accretion rate, indicating that accretion is not sensitive to
the properties of the interstellar medium of the galaxy on large scales.
However, in the red population accretion rate and gas fraction do correlate.
The measured gas fractions in this population are not too different from the
ones expected from a stellar mass loss origin, implying that the fuel supply in
the red AGN population could be a mixture of mass loss from stars and gas
present in disks. | Potential signature of a quadrupolar Hubble expansion in Pantheon+
supernovae: The assumption of isotropy -- that the Universe looks the same in all
directions on large scales -- is fundamental to the standard cosmological
model. This model forms the building blocks of essentially all of our
cosmological knowledge to date. It is therefore critical to empirically test in
which regimes its core assumptions hold. Anisotropies in the cosmic expansion
are expected on small scales due to nonlinear structures in the late Universe,
however, the extent to which these anisotropies might impact our low-redshift
observations remains to be fully tested. In this paper, we use fully general
relativistic simulations to calculate the expected local anisotropic expansion
and identify the dominant multipoles in cosmological parameters to be the
quadrupole in the Hubble parameter and the dipole in the deceleration
parameter. We constrain these multipoles simultaneously in the new Pantheon+
supernova compilation. The fiducial analysis is done in the rest frame of the
CMB with peculiar velocity corrections. Under the fiducial range of redshifts
in the Hubble flow sample, we find a $\sim 2\sigma$ deviation from isotropy. We
constrain the eigenvalues of the quadrupole in the Hubble parameter to be
$\lambda_1 =0.021\pm{ 0.011}$ and $ {\lambda_2= 3.15\times 10^{-5}}\pm 0.012$
and place a $1\sigma$ upper limit on its amplitude of $2.88\%$. We find no
significant dipole in the deceleration parameter, finding constraints of
$q_{\rm dip} = 4.5^{+1.9}_{-5.4}$. However, in the rest frame of the CMB
without corrections, we find $ q_{ \rm dip} = 9.6^{+4.0}_{-6.9}$, a $>2\sigma$
positive amplitude. We also investigate the impact of these anisotropies on the
Hubble tension. We find a maximal shift of $0.30$ km s$^{-1}$ Mpc$^{-1}$ in the
monopole of the Hubble parameter and conclude that local anisotropies are
unlikely to fully explain the observed tension. |
The Evolution and Mass Dependence of Galaxy Cluster Pressure Profiles at
0.05 $\le z \le$ 0.60 and $4 \times 10^{14}$ M$_{\odot}$ $\le
\textrm{M}_{500} \le 30 \times 10^{14}$ M$_{\odot}$: We have combined X-ray observations from Chandra with Sunyaev-Zel'dovich (SZ)
effect data from Planck and Bolocam to measure intra-cluster medium pressure
profiles from 0.03R$_{500}$ $\le$ R $\le$ 5R$_{500}$ for a sample of 21 low-$z$
galaxy clusters with a median redshift $\langle z \rangle = 0.08$ and a median
mass $\langle \textrm{M}_{500} \rangle = 6.1 \times 10^{14}$ M$_{\odot}$ and a
sample of 19 mid-$z$ galaxy clusters with $\langle z \rangle = 0.50$ and
$\langle \textrm{M}_{500} \rangle = 10.6 \times 10^{14}$ M$_{\odot}$. The mean
scaled pressure in the low-$z$ sample is lower at small radii and higher at
large radii, a trend that is accurately reproduced in similarly selected
samples from The300 simulations. This difference appears to be primarily due to
dynamical state at small radii, evolution at intermediate radii, and a
combination of evolution and mass dependence at large radii. Furthermore, the
overall flattening of the mean scaled pressure profile in the low-$z$ sample
compared to the mid-$z$ sample is consistent with expectations due to
differences in mass accretion rate and the fractional impact of feedback
mechanisms. In agreement with previous studies, the fractional scatter about
the mean scaled pressure profile reaches a minimum of $\simeq 20$ per cent near
0.5R$_{500}$. This scatter is consistent between the low-$z$ and mid-$z$
samples at all radii, suggesting it is not strongly impacted by sample
selection, and this general behavior is reproduced in The300 simulations.
Finally, analytic functions that approximately describe the mass and redshift
trends in mean pressure profile shape are provided. | The LyA-LyC Connection: Evidence for an Enhanced Contribution of
UV-faint Galaxies to Cosmic Reionization: The escape of ionizing Lyman Continuum (LyC) photons requires the existence
of low-N_HI sightlines, which also promote escape of Lyman-Alpha (Lya). We use
a suite of 2500 Lya Monte-Carlo radiative transfer simulations through models
of dusty, clumpy interstellar (`multiphase') media from Gronke & Dijkstra
(2016), and compare the escape fractions of Lya [f_esc(Lya)] and LyC radiation
[f_esc(LyC)]. We find that f_esc(LyC) and f_esc(Lya) are correlated: galaxies
with a low f_esc(Lya) consistently have a low f_esc(LyC), while galaxies with a
high f_esc(Lya) exhibit a large dispersion in f_esc(LyC). We argue that there
is increasing observational evidence that Lya escapes more easily from UV-faint
galaxies. The correlation between f_esc(LyC) and f_esc(Lya) then implies that
UV-faint galaxies contribute more to the ionizing background than implied by
the faint-end slope of the UV-luminosity function. In multiphase gases, the
ionizing escape fraction is most strongly affected by the cloud covering
factor, f_cl, which implies that f_esc(LyC) is closely connected to the
observed Lya spectral line shape. Specifically, LyC emitting galaxies typically
having narrower, more symmetric line profiles. This prediction is qualitatively
similar to that for `shell models'. |
Evidence for spin alignment of spiral and elliptical/S0 galaxies in
filaments: Galaxies are not distributed randomly in the cosmic web but are instead
arranged in filaments and sheets surrounding cosmic voids. Observationally
there is still no convincing evidence of a link between the properties of
galaxies and their host structures. However, by the tidal torque theory (our
understanding of the origin of galaxy angular momentum), such a link should
exist. Using the presently largest spectroscopic galaxy redshift survey (SDSS)
we study the connection between the spin axes of galaxies and the orientation
of their host filaments.
We use a three dimensional field of orientations to describe cosmic
filaments. To restore the inclination angles of galaxies, we use a 3D
photometric model of galaxies that gives these angles more accurately than
traditional 2D models.
We found evidence that the spin axes of bright spiral galaxies have a weak
tendency to be aligned parallel to filaments. For elliptical/S0 galaxies, we
have a statistically significant result that their spin axes are aligned
preferentially perpendicular to the host filaments; we show that this signal
practically does not depend on the accuracy of the estimated inclination angles
for elliptical/S0 galaxies. | Optical emission line properties of a sample of the broad-line AGNs: the
Baldwin effect and eigenvector 1: We divide a sample of 302 type-1 AGNs into two subsamples based on the narrow
line [OIII]/Hbeta_{NLR} ratio, since we expect that there will be a stronger
starburst (HII region) contribution to the narrow line emission for
R=log([OIII]/Hbeta_{NLR})<0.5. For the two samples we {find significant
differences in correlations between} spectral properties of objects with
$R<0.5$ and R>0.5. {We find similar differences when we divided the sample
based on the FWHM ratios of [OIII] and broad Hbeta lines
(R_1=log(FWHM[OIII]/FWHM Hbeta_broad)^>_<-0.8), i.e. similar correlations
between R>0.5 and R_1<-0.8 subsamples from one side and R<0.5 and R_1>-0.8
subsamples from the other side.} The most interesting difference is in the
correlation between the broad Hbeta FWHM and luminosity in the R<0.5 (R_1>-0.8)
sample that indicates a connection between the BLR kinematics and
photoionization source. We discuss possible effects which can cause such
differences in spectral properties of two subsamples. |
3D-MHD simulations of the evolution of magnetic fields in FR II radio
sources: 3D-MHD numerical simulations of bipolar, hypersonic, weakly magnetized jets
and synthetic synchrotron observations are presented to study the structure and
evolution of magnetic fields in FR II radio sources. The magnetic field setup
in the jet is initially random. The power of the jets as well as the
observational viewing angle are investigated. We find that synthetic
polarization maps agree with observations and show that magnetic fields inside
the sources are shaped by the jets' backflow. Polarimetry statistics correlates
with time, the viewing angle and the jet-to-ambient density contrast. The
magnetic structure inside thin elongated sources is more uniform than for ones
with fatter cocoons. Jets increase the magnetic energy in cocoons, in
proportion to the jet velocity. Both, filaments in synthetic emission maps and
3D magnetic power spectra suggest that turbulence develops in evolved sources. | CMB Angular Power Spectrum from Correlated Primordial Fluctuation: The usual inflationary scenario predicts a Gaussian random primordial density
fluctuation, different Fourier modes of which do not correlate with each other.
In this paper we propose a correlation between these different modes. A simple
case is that these different Fourier modes correlate with each other following
a Gaussian function. For such a primordial density fluctuation we calculate the
CMB angular power spectrum and find that its amplitude decreases but the
decrease is different for different $l$. This feature can be used to constrain
the the correlation strength from the real data. |
Polarizations of CMB and the Hubble tension: Future precision measurements of CMB polarizations can shed new light on the
problem so called Hubble tension. The Hubble tension comes from the difference
of the evolutions of the Hubble parameter which are determined with two
different distance ladders. The standard distance ladder with the observation
of Cepheid variables and type Ia supernovae gives larger values of the Hubble
constant, and the inverse distance ladder with the observation of the baryon
acoustic oscillations both in the CMB and in the clustering of galaxies gives
smaller values of the Hubble constant. These different evolutions of the Hubble
parameter indicate different evolutions of the free electron density in the
process of the reionization of the universe and different magnitudes of low-l
polarizations of the CMB, since these polarizations are mainly produced through
the Thomson scattering of CMB photons off these free electrons. We investigate
the effect on CMB E-mode and B-mode polarizations of l < 12 assuming
non-trivially time-dependent equation of state of dark energy. We find that the
case of the standard distance ladder gives higher power of polarizations than
the prediction in the LambdaCDM model. | What can the spatial distribution of galaxy clusters tell about their
scaling relations?: We aim to quantify the capability of the inhomogeneous distribution of galaxy
clusters, represented by the two-point statistics in Fourier space, to retrieve
information on the underlying scaling relations. We make a case study using the
mass X-ray luminosity scaling relation for galaxy clusters and study its impact
on the clustering pattern of these objects. We define the luminosity-weighted
power spectrum and introduce the luminosity power spectrum as direct assessment
of the clustering of the property of interest, in our case, the cluster X-ray
luminosity. Using a suite of halo catalogs extracted from N-body simulations
and realistic estimates of the mass X-ray luminosity relation, we measured
these statistics with their corresponding covariance matrices. By carrying out
a Fisher matrix analysis, we quantified the content of information (by means of
a figure-of merit) encoded in the amplitude, shape, and full shape of our
probes for two-point statistics. The full shape of the luminosity power
spectrum, when analyzed up to scales of k~0.2 h/Mpc, yields a figure of merit
which is two orders of magnitude above the figure obtained from the unweighted
power spectrum, and only one order of magnitude below the value encoded in
X-ray luminosity function estimated from the same sample. This is a significant
improvement over the analysis developed with the standard (i.e., unweighted)
clustering probes. The measurements of the clustering of galaxy clusters and
its explicit dependence on the cluster intrinsic properties can contribute to
improving the degree of knowledge regarding the underlying links between
cluster observables and the cluster masses (Abridged). |
Three-Dimensional Simulations of Bi-Directed Magnetohydrodynamic Jets
Interacting with Cluster Environments: We report on a series of three-dimensional magnetohydrodynamic simulations of
active galactic nucleus (AGN) jet propagation in realistic models of magnetized
galaxy clusters. We are primarily interested in the details of energy transfer
between jets and the intracluster medium (ICM) to help clarify what role such
flows could have in the reheating of cluster cores. Our simulated jets feature
a range of intermittency behaviors, including intermittent jets that
periodically switch on and off and one model jet that shuts down completely,
naturally creating a relic plume. The ICM into which these jets propagate
incorporates tangled magnetic field geometries and density substructure
designed to mimic some likely features of real galaxy clusters. We find that
our jets are characteristically at least 60% efficient at transferring thermal
energy to the ICM. Irreversible heat energy is not uniformly distributed,
however, instead residing preferentially in regions very near the jet/cocoon
boundaries. While intermittency affects the details of how, when, and where
this energy is deposited, all of our models generically fail to heat the
cluster cores uniformly. Both the detailed density structure and nominally weak
magnetic fields in the ICM play interesting roles in perturbing the flows,
particularly when the jets are non-steady. Still, this perturbation is never
sufficient to isotropize the jet energy deposition, suggesting that some other
ingredient is required for AGN jets to successfully reheat cluster cores. | Intensity Mapping of the [CII] Fine Structure Line during the Epoch of
Reionization: The atomic CII fine-structure line is one of the brightest lines in a typical
star-forming galaxy spectrum with a luminosity ~ 0.1% to 1% of the bolometric
luminosity. It is potentially a reliable tracer of the dense gas distribution
at high redshifts and could provide an additional probe to the era of
reionization. By taking into account of the spontaneous, stimulated and
collisional emission of the CII line, we calculate the spin temperature and the
mean intensity as a function of the redshift. When averaged over a
cosmologically large volume, we find that the CII emission from ionized carbon
in individual galaxies is larger than the signal generated by carbon in the
intergalactic medium (IGM). Assuming that the CII luminosity is proportional to
the carbon mass in dark matter halos, we also compute the power spectrum of the
CII line intensity at various redshifts. In order to avoid the contamination
from CO rotational lines at low redshift when targeting a CII survey at high
redshifts, we propose the cross-correlation of CII and 21-cm line emission from
high redshifts. To explore the detectability of the CII signal from
reionization, we also evaluate the expected errors on the CII power spectrum
and CII-21 cm cross power spectrum based on the design of the future milimeter
surveys. We note that the CII-21 cm cross power spectrum contains interesting
features that captures physics during reionization, including the ionized
bubble sizes and the mean ionization fraction, which are challenging to measure
from 21-cm data alone. We propose an instrumental concept for the reionization
CII experiment targeting the frequency range of $\sim$ 200 to 300 GHz with 1, 3
and 10 meter apertures and a bolometric spectrometer array with 64 independent
spectral pixels with about 20,000 bolometers. |
NECOLA: Towards a Universal Field-level Cosmological Emulator: We train convolutional neural networks to correct the output of fast and
approximate N-body simulations at the field level. Our model, Neural Enhanced
COLA --NECOLA--, takes as input a snapshot generated by the computationally
efficient COLA code and corrects the positions of the cold dark matter
particles to match the results of full N-body Quijote simulations. We quantify
the accuracy of the network using several summary statistics, and find that
NECOLA can reproduce the results of the full N-body simulations with
sub-percent accuracy down to $k\simeq1~h{\rm Mpc}^{-1}$. Furthermore, the
model, that was trained on simulations with a fixed value of the cosmological
parameters, is also able to correct the output of COLA simulations with
different values of $\Omega_{\rm m}$, $\Omega_{\rm b}$, $h$, $n_s$, $\sigma_8$,
$w$, and $M_\nu$ with very high accuracy: the power spectrum and the
cross-correlation coefficients are within $\simeq1\%$ down to $k=1~h{\rm
Mpc}^{-1}$. Our results indicate that the correction to the power spectrum from
fast/approximate simulations or field-level perturbation theory is rather
universal. Our model represents a first step towards the development of a fast
field-level emulator to sample not only primordial mode amplitudes and phases,
but also the parameter space defined by the values of the cosmological
parameters. | A common explanation of the Hubble tension and anomalous cold spots in
the CMB: The standard cosmological paradigm narrates a reassuring story of a universe
currently dominated by an enigmatic dark energy component. Disquietingly, its
universal explaining power has recently been challenged by, above all, the
$\sim4\sigma$ tension in the values of the Hubble constant. Another, less
studied anomaly is the repeated observation of integrated Sachs-Wolfe imprints
$\sim5\times$ stronger than expected in the $\Lambda$CDM model from R>100
$Mpc/h$ super-structures. Here we show that the inhomogeneous AvERA model of
emerging curvature is capable of telling a plausible albeit radically different
story that explains both observational anomalies without dark energy. We
demonstrate that while stacked imprints of R>100 $Mpc/h$ supervoids in cosmic
microwave background temperature maps can discriminate between the AvERA and
$\Lambda$CDM models, their characteristic differences may remain hidden using
alternative void definitions and stacking methodologies. Testing the extremes,
we then also show that the CMB Cold Spot can plausibly be explained in the
AvERA model as an ISW imprint. The coldest spot in the AvERA map is aligned
with multiple low-$z$ supervoids with R>100 $Mpc/h$ and central underdensity
$\delta_{0}\approx-0.3$, resembling the observed large-scale galaxy density
field in the Cold Spot area. We hence conclude that the anomalous imprint of
supervoids may well be the canary in the coal mine, and existing observational
evidence for dark energy should be re-interpreted to further test alternative
models. |
Solution for cosmological observables in the Starobinsky model of
inflation: This paper focuses on the Starobinsky model of inflation. We derive solutions
for various cosmological observables, such as the scalar spectral index $n_s$,
the tensor-to-scalar ratio $r$ and their runnings, as well as the number of
$e$-folds of inflation, reheating, and radiation with minimal assumptions. We
establish an equation that connects inflation and reheating, which can be
solved for the spectral index $n_s$. Using consistency relations of the model,
we determine the other observables, the number of $e$-folds during inflation
$N_k$, and the number of $e$-folds during reheating $N_{re}$. The impact of
reheating on inflation is explored by constraining the equation of state
parameter $\omega_{re}$ at the end of reheating. We find remarkable agreement
between the Starobinsky model and current measurements of the power spectrum of
primordial curvature perturbations and the present bounds on the spectrum of
primordial gravitational waves. | Photo-zSNthesis: Converting Type Ia Supernova Lightcurves to Redshift
Estimates via Deep Learning: Upcoming photometric surveys will discover tens of thousands of Type Ia
supernovae (SNe Ia), vastly outpacing the capacity of our spectroscopic
resources. In order to maximize the science return of these observations in the
absence of spectroscopic information, we must accurately extract key
parameters, such as SN redshifts, with photometric information alone. We
present Photo-zSNthesis, a convolutional neural network-based method for
predicting full redshift probability distributions from multi-band supernova
lightcurves, tested on both simulated Sloan Digital Sky Survey (SDSS) and Vera
C. Rubin Legacy Survey of Space and Time (LSST) data as well as observed SDSS
SNe. We show major improvements over predictions from existing methods on both
simulations and real observations as well as minimal redshift-dependent bias,
which is a challenge due to selection effects, e.g. Malmquist bias.
Specifically, we show a 61x improvement in prediction bias <Delta z> on
PLAsTiCC simulations and 5x improvement on real SDSS data compared to results
from a widely used photometric redshift estimator, LCFIT+Z. The PDFs produced
by this method are well-constrained and will maximize the cosmological
constraining power of photometric SNe Ia samples. |
The Delay of Population III Star Formation by Supersonic Streaming
Velocities: It has recently been demonstrated that coherent relative streaming velocities
of order 30 km / s between dark matter and gas permeated the universe on scales
below a few Mpc directly after recombination. We here use a series of
high-resolution moving-mesh calculations to show that these supersonic motions
significantly influence the virialization of the gas in minihalos, and delay
the formation of the first stars. As the gas streams into minihalos with bulk
velocities around 1 km / s at z ~ 20, the additional momentum and energy input
reduces the gas fractions and central densities of the halos, increasing the
typical virial mass required for efficient cooling by a factor of three, and
delaying Population III star formation by dz ~ 4. Since the distribution of the
magnitude of the streaming velocities is narrowly peaked around a
non-negligible value, this effect is important in most regions of the universe.
As a consequence, the increased minimum halo mass implies a reduction of the
absolute number of minihalos that can be expected to cool and form Population
III stars by up to an order of magnitude. We further find that the streaming
velocities increase the turbulent velocity dispersion of the minihalo gas,
which could affect its ability to fragment and hence alter the mass function of
the first stars. | Diffuse Radio Emission in Abell 754: We present a low frequency study of the diffuse radio emission in the galaxy
cluster A754. We present new 150 MHz image of the galaxy cluster A754 made with
the Giant Metrewave Radio Telescope (GMRT) and discuss the detection of 4
diffuse features. We compare the 150 MHz image with the images at 74, 330 and
1363 MHz; one new diffuse feature is detected. The flux density upperlimits at
330 and 1363 MHz imply a synchrotron spectral index, $\alpha > 2$, ($S\propto
\nu^{-\alpha}$) for the new feature. The 'west relic' detected at 74 MHz
(Kassim et al 2001) is not detected at 150 MHz and is thus consistent with its
non-detection at 1363 MHz (Bacchi et al 2003) and 330 MHz(Kassim et al 2001).
Integrated spectra of all the diffuse features are presented. The fourth
diffuse feature is located along the proposed merger axis (Zabludoff et al
1995) in A754 and 0.7 Mpc away from the peak of X-ray emission. We have made
use of the framework of adiabatic compression model (Ensslin & Gopal-Krishna
2001) to obtain spectra. We show that the spectrum of the fourth diffuse
feature is consistent with that of a cocoon of a radio galaxy lurking for about
$9\times10^{7}$ yr; no shock compression is required. The other three diffuse
emission have spectra steeper than 1.5 and could be cocoons lurking for longer
time. We discuss other possibilities such as shocks and turbulent
reacceleration being responsible for the diffuse emission in A754. |
Opening the reheating box in multifield inflation: The robustness of multi-field inflation to the physics of reheating is
investigated. In order to carry out this study, reheating is described in
detail by means of a formalism which tracks the evolution of scalar fields and
perfect fluids in interaction (the inflatons and their decay products). This
framework is then used to establish the general equations of motion of the
background and perturbative quantities controlling the evolution of the system
during reheating. Next, these equations are solved exactly by means of a new
numerical code. Moreover, new analytical techniques, allowing us to interpret
and approximate these solutions, are developed. As an illustration of a
physical prediction that could be affected by the micro-physics of reheating,
the amplitude of non-adiabatic perturbations in double inflation is considered.
It is found that ignoring the fine-structure of reheating, as usually done in
the standard approach, can lead to differences as big as $\sim 50\%$, while our
semi-analytic estimates can reduce this error to $\sim 10\%$. We conclude that,
in multi-field inflation, tracking the perturbations through the details of the
reheating process is important and, to achieve good precision, requires the use
of numerical calculations. | Inferring the IGM thermal history during reionisation with the
Lyman-$α$ forest power spectrum at redshift $z \simeq 5$: We use cosmological hydrodynamical simulations to assess the feasibility of
constraining the thermal history of the intergalactic medium during
reionisation with the Ly$\alpha$ forest at $z\simeq5$. The integrated thermal
history has a measureable impact on the transmitted flux power spectrum that
can be isolated from Doppler broadening at this redshift. We parameterise this
using the cumulative energy per proton, $u_0$, deposited into a gas parcel at
the mean background density, a quantity that is tightly linked with the gas
density power spectrum in the simulations. We construct mock observations of
the line of sight Ly$\alpha$ forest power spectrum and use a Markov Chain Monte
Carlo approach to recover $u_{0}$ at redshifts $5 \leq z \leq 12$. A
statistical uncertainty of $\sim 20$ per cent is expected (at 68 per cent
confidence) at $z\simeq 5$ using high resolution spectra with a total redshift
path length of $\Delta z=4$ and a typical signal-to-noise ratio of $\rm S/N=15$
per pixel. Estimates for the expected systematic uncertainties are comparable,
such that existing data should enable a measurement of $u_0$ to within $\sim
30$ per cent. This translates to distinguishing between reionisation scenarios
with similar instantaneous temperatures at $z\simeq 5$, but with an energy
deposited per proton that differs by $2$-$3\, \rm eV$ over the redshift
interval $5\leq z \leq 12$. For an initial temperature of $T\sim 10^{4}\rm\,K$
following reionisation, this corresponds to the difference between early
($z_{\rm re}=12$) and late ($z_{\rm re}=7$) reionisation in our models. |
On the power spectrum generated during inflation: Recently there have been differing viewpoints on how to evaluate the
curvature power spectrum generated during inflation. Since the primordial
curvature power spectrum is the seed for structure formation and provides a
link between observations and inflationary parameters, it is important to
resolve any disagreements over the expression for the power spectrum. In this
article we discuss these differing viewpoints and indicate issues that are
relevant to both approaches. We then argue why the standard expression is
valid. | Mid-IR Luminosities and UV/Optical Star Formation Rates at z<1.4: UV continuum and mid-IR emission constitute two widely used star formation
indicators at intermediate and high redshifts. We study 2430 galaxies with
z<1.4 in the Extended Groth Strip with MIPS 24 mic observations from FIDEL,
spectroscopy from DEEP2, and UV, optical, and near-IR photometry from AEGIS.
The data are coupled with stellar population models and Bayesian SED fitting to
estimate dust-corrected SFRs. In order to probe the dust heating from stellar
populations of various ages, the derived SFRs were averaged over various
timescales--from 100 Myr for "current" SFR to 1--3 Gyr for long-timescale SFRs.
These SED-based UV/optical SFRs are compared to total infrared luminosities
extrapolated from 24 mic observations. We find that for the blue, actively star
forming galaxies the correlation between the IR luminosity and the UV/optical
SFR shows a decrease in scatter when going from shorter to longer SFR-averaging
timescales. We interpret this as the greater role of intermediate age stellar
populations in heating the dust than what is typically assumed. This holds over
the entire redshift range. Many so-called green valley galaxies are simply
dust-obscured actively star-forming galaxies. However, there exist 24
mic-detected galaxies, some with L>10^11 L_sun, yet with little current star
formation. For them a reasonable amount of dust absorption of stellar light is
sufficient to produce the observed levels of IR. In our sample optical and
X-ray AGNs do not contribute on average more than ~50% to the mid-IR
luminosity, and we see no evidence for a large population of "IR excess"
galaxies (Abridged). |
Spectral Energy Distribution Models for Low-luminosity Active Galactic
Nuclei in LINERs: Low-luminosity active galactic nuclei (LLAGNs) represent the bulk of the AGN
population in the present-day universe and they trace the low-level accreting
supermassive black holes. In order to probe the accretion and jet physical
properties in LLAGNs as a class, we model the broadband radio to X-rays
spectral energy distributions (SEDs) of 21 LLAGNs in low-ionization nuclear
emission-line regions (LINERs) with a coupled accretion-jet model. The
accretion flow is modeled as an inner ADAF outside of which there is a
truncated standard thin disk. We find that the radio emission is severely
underpredicted by ADAF models and is explained by the relativistic jet. The
origin of the X-ray radiation in most sources can be explained by three
distinct scenarios: the X-rays can be dominated by emission from the ADAF, or
the jet, or the X-rays can arise from a jet-ADAF combination in which both
components contribute to the emission with similar importance. For 3 objects
both the jet and ADAF fit equally well the X-ray spectrum and can be the
dominant source of X-rays whereas for 11 LLAGNs a jet-dominated model accounts
better than the ADAF-dominated model for the data. The individual and average
SED models that we computed can be useful for different studies of the nuclear
emission of LLAGNs. From the model fits, we estimate important parameters of
the central engine powering LLAGNs in LINERs, such as the mass accretion rate
and the mass-loss rate in the jet and the jet power - relevant for studies of
the kinetic feedback from jets. | Toward A Consistent Picture For CRESST, CoGeNT and DAMA: Three dark matter direct detection experiments (DAMA/LIBRA, CoGeNT, and
CRESST-II) have each reported signals which are not consistent with known
backgrounds, but resemble that predicted for a dark matter particle with a mass
of roughly $\sim$10 GeV and an elastic scattering cross section with nucleons
of $\sim$$10^{-41}$--$10^{-40}$ cm$^2$. In this article, we compare the signals
of these experiments and discuss whether they can be explained by a single
species of dark matter particle, without conflicting with the constraints of
other experiments. We find that the spectrum of events reported by CoGeNT and
CRESST-II are consistent with each other and with the constraints from CDMS-II,
although some tension with xenon-based experiments remains. Similarly, the
modulation signals reported by DAMA/LIBRA and CoGeNT appear to be compatible,
although the corresponding amplitude of the observed modulations are a factor
of at least a few higher than would be naively expected, based on the event
spectra reported by CoGeNT and CRESST-II. This apparent discrepancy could
potentially be resolved if tidal streams or other non-Maxwellian structures are
present in the local distribution of dark matter. |
Spatial Distribution of Intracluster Light versus Dark Matter in Horizon
Run 5: One intriguing approach for studying the dynamical evolution of galaxy
clusters is to compare the spatial distributions among various components, such
as dark matter, member galaxies, gas, and intracluster light (ICL). Utilizing
the recently introduced Weighted Overlap Coefficient (WOC)
\citep{2022ApJS..261...28Y}, we analyze the spatial distributions of components
within 174 galaxy clusters ($M_{\rm tot}> 5 \times 10^{13} M_{\odot}$,
$z=0.625$) at varying dynamical states in the cosmological hydrodynamical
simulation Horizon Run 5. We observe that the distributions of gas and the
combination of ICL with the brightest cluster galaxy (BCG) closely resembles
the dark matter distribution, particularly in more relaxed clusters,
characterized by the half-mass epoch. The similarity in spatial distribution
between dark matter and BCG+ICL mimics the changes in the dynamical state of
clusters during a major merger. Notably, at redshifts $>$ 1, BCG+ICL traced
dark matter more accurately than the gas. Additionally, we examined the
one-dimensional radial profiles of each component, which show that the BCG+ICL
is a sensitive component revealing the dynamical state of clusters. We propose
a new method that can approximately recover the dark matter profile by scaling
the BCG+ICL radial profile. Furthermore, we find a recipe for tracing dark
matter in unrelaxed clusters by including the most massive satellite galaxies
together with BCG+ICL distribution. Combining the BCG+ICL and the gas
distribution enhances the dark matter tracing ability. Our results imply that
the BCG+ICL distribution is an effective tracer for the dark matter
distribution, and the similarity of spatial distribution may be a useful probe
of the dynamical state of a cluster. | Cosmological test of local position invariance from the asymmetric
galaxy clustering: The local position invariance (LPI) is one of the three major pillars of
Einstein equivalence principle, ensuring the space-time independence on the
outcomes of local experiments. The LPI has been tested by measuring the
gravitational redshift effect in various depths of gravitational potentials. We
propose a new cosmological test of the LPI by observing the asymmetry in the
cross-correlation function between different types of galaxies, which
predominantly arises from the gravitational redshift effect induced by the
gravitational potential of halos at which the galaxies reside. We show that the
ongoing and upcoming galaxy surveys can give a fruitful constraint on the
LPI-violating parameter, $\alpha$, at distant universes (redshift
$z\sim0.1-1.8$) over the cosmological scales (separation $s\sim5-10\, {\rm
Mpc}/h$) that have not yet been explored, finding that the expected upper limit
on $\alpha$ can reach $0.03$. |
Testing the cosmic conservation of photon number with type Ia supernovae
and ages of old objects: In this paper, we obtain luminosity distances by using ages of 32 old passive
galaxies distributed over the redshift interval $0.11 < z < 1.84$ and test the
cosmic conservation of photon number by comparing them with 580 distance moduli
of type Ia supernovae (SNe Ia) from the so-called Union 2.1 compilation. Our
analyses are based on the fact that the method of obtaining ages of galaxies
relies on the detailed shape of galaxy spectra but not on galaxy luminosity.
Possible departures from cosmic conservation of photon number is parametrized
by $\tau(z) = 2 \epsilon z$ and $\tau(z) = \epsilon z/(1+z)$ (for $\epsilon =0$
the conservation of photon number is recovered). We find
$\epsilon=0.016^{+0.078}_{-0.075}$ from the first parametrization and
$\epsilon=-0.18^{+0.25}_{-0.24}$ from the second parametrization, both limits
at 95\% c.l. In this way, no significant departure from cosmic conservation of
photon number is verified. In addition, by considering the total age as
inferred from Planck (2015) analysis, we find the incubation time
$t_{inc}=1.66\pm0.29$ Gyr and $t_{inc}=1.23\pm0.27$ Gyr at 68\% c.l. for each
parametrization, respectively.} | Understanding the nature of luminous red galaxies (LRGs): Connecting
LRGs to central and satellite subhalos: We develop a novel abundance matching method to construct a mock catalog of
luminous red galaxies (LRGs) in SDSS, using catalogs of halos and subhalos in
N-body simulations for a LCDM model. Motivated by observations suggesting that
LRGs are passively-evolving, massive early-type galaxies with a typical age
>5Gyr, we assume that simulated halos at z=2 (z2-halo) are progenitors for
LRG-host subhalos observed today, and we label the most tightly bound particles
in each progenitor z2-halo as LRG ``stars''. We then identify the subhalos
containing these stars to z=0.3 (SDSS redshift) in descending order of the
masses of z2-halos until the comoving number density of the matched subhalos
becomes comparable to the measured number density of SDSS LRGs, n=10^{-4}
(h/Mpc)^3. Once the above prescription is determined, our only free parameter
is the number density of halos identified at z=2 and this parameter is fixed to
match the observed number density at z = 0.3. By tracing subsequent merging and
assembly histories of each progenitor z2-halo, we can directly compute, from
the mock catalog, the distributions of central and satellite LRGs and their
internal motions in each host halo at z=0.3. While the SDSS LRGs are galaxies
selected by the magnitude and color cuts from the SDSS images and are not
necessarily a stellar-mass-selected sample, our mock catalog reproduces a host
of SDSS measurements: the halo occupation distribution for central and
satellite LRGs, the projected auto-correlation function of LRGs, the
cross-correlation of LRGs with shapes of background galaxies (LRG-galaxy weak
lensing), and the nonlinear redshift-space distortion effect, the Finger-of-God
effect, in the angle-averaged redshift-space power spectrum. |
Constraining holographic inflation with WMAP: In a class of recently proposed models, the early universe is strongly
coupled and described holographically by a three-dimensional, weakly coupled,
super-renormalizable quantum field theory. This scenario leads to a power
spectrum of scalar perturbations that differs from the usual empirical LCDM
form and the predictions of generic models of single field, slow roll
inflation. This spectrum is characterized by two parameters: an amplitude, and
a parameter g related to the coupling constant of the dual theory. We estimate
these parameters, using WMAP and other astrophysical data. We compute Bayesian
evidence for both the holographic model and standard LCDM and find that their
difference is not significant, although LCDM provides a somewhat better fit to
the data. However, it appears that Planck will permit a definitive test of this
holographic scenario. | Test of the Einstein equivalence principle with spectral distortions in
the cosmic microwave background: The Einstein Equivalence Principle~(EEP) can be verified by the measurement
of the spectral distortions of the Cosmic Microwave Background (CMB). The
existence of energy-dependency in the cosmological redshift effect means the
EEP violation. Introducing the energy-dependent Friedmann-Robertson-Walker
metric motivated by rainbow gravity, we show that the energy-dependent redshift
effect causes the CMB spectral distortions. Assuming the simple
energy-dependent form of the metric, we evaluate the distortions. From the
COBE/FIRAS bound, we find that the deviation degree from the EEP, which is
comparable to the difference of the parameterized-post-Newtonian parameter
"gamma" in energy, is less than 10^{-9} at the CMB energy scale. |
Type-Ia supernova rates and the progenitor problem, a review: The identity of the progenitor systems of type-Ia supernovae (SNe Ia) is a
major unsolved problem in astrophysics. SN Ia rates are providing some striking
clues. We review the basics of SN rate measurement, preach about some sins of
SN rate measurement and analysis, and illustrate one of these sins with an
analogy about Martian scientists. We review the recent progress in measuring SN
Ia rates in various environments and redshifts, and their use to reconstruct
the SN Ia delay time distribution (DTD) -- the SN rate versus time that would
follow a hypothetical brief burst of star formation. A good number of DTD
measurements, using a variety of methods, appear to be converging. At delays
1<t<10 Gyr, these measurements show a similar, ~t^-1, power-law shape. The DTD
peaks at the shortest delays probed, although there is still some uncertainty
regarding its precise shape at t<1 Gyr. At face value, this result supports the
idea of a double-degenerate progenitor origin for SNe Ia. Single-degenerate
progenitors may still play a role in producing short-delay SNe Ia, or perhaps
all SNe Ia, if the red-giant donor channel is more efficient than found by most
theoretical models. Apart from the DTD shape, the DTD normalization enjoys
fairly good agreement (though perhaps some tension), among the various
measurements, with a Hubble-time-integrated DTD value of about 2+/- 1 SNe Ia
per 1000 Msun (stellar mass formed with a low-mass-turnover IMF). A recent
attempt to characterize the local white dwarf binary population suggests that
the white dwarf merger rate can explain the Galactic SN Ia rate, if sub-Chandra
mergers lead to SN Ia events. We conclude by pointing to some future directions
that should lead to progress in the field, including measurement of the
bivariate (delay and stretch) SN Ia response function . | How the Dark Energy Can Reconcile \textit{Planck} with Local
Determination of the Hubble Constant: We try to reconcile the tension between the local 2.4\% determination of
Hubble constant and its global determination by $\textit{Planck}$ CMB data and
BAO data through modeling the dark energy variously. We find that the
chi-square is significantly reduced by $\Delta\chi^2_\text{all}=-6.76$ in the
redshift-binned dark energy model where the $68\%$ limits of the equation of
state of dark energy read $w(0\leq z\leq 0.1)=-1.958_{-0.508}^{+0.509}$,
$w(0.1< z\leq 1.5)=-1.006_{-0.082}^{+0.092}$, and here $w(z>1.5)$ is fixed to
$-1$. |
PICS: Simulations of Strong Gravitational Lensing in Galaxy Clusters: Gravitational lensing has become one of the most powerful tools available for
investigating the 'dark side' of the universe. Cosmological strong
gravitational lensing, in particular, probes the properties of the dense cores
of dark matter halos over decades in mass and offers the opportunity to study
the distant universe at flux levels and spatial resolutions otherwise
unavailable. Studies of strongly-lensed variable sources offer yet further
scientific opportunities. One of the challenges in realizing the potential of
strong lensing is to understand the statistical context of both the individual
systems that receive extensive follow-up study, as well as that of the larger
samples of strong lenses that are now emerging from survey efforts. Motivated
by these challenges, we have developed an image-simulation pipeline, PICS
(Pipeline for Images of Cosmological Strong lensing) to generate realistic
strong gravitational lensing signals from group and cluster scale lenses. PICS
uses a low-noise and unbiased density estimator based on (resampled) Delaunay
Tessellations to calculate the density field; lensed images are produced by
ray-tracing images of actual galaxies from deep Hubble Space Telescope
observations. Other galaxies, similarly sampled, are added to fill in the light
cone. The pipeline further adds cluster-member galaxies and foreground stars
into the lensed images. The entire image ensemble is then observed using a
realistic point spread function which includes appropriate detector artifacts
for bright stars. Noise is further added, including such non-Gaussian elements
as noise window-paning from mosaiced observations, residual bad pixels, and
cosmic rays. The aim is to produced simulated images that appear identical - to
the eye (expert or otherwise) - to real observations in various imaging
surveys. | Modeling the reconstructed BAO in Fourier space: The density field reconstruction technique, which was developed to partially
reverse the nonlinear degradation of the Baryon Acoustic Oscillation (BAO)
feature in the galaxy redshift surveys, has been successful in substantially
improving the cosmology constraints from recent galaxy surveys such as Baryon
Oscillation Spectroscopic Survey (BOSS). We estimate the efficiency of the
reconstruction method as a function of various reconstruction details. To
directly quantify the BAO information in nonlinear density fields before and
after reconstruction, we calculate the cross-correlations (i.e., propagators)
of the pre(post)-reconstructed density field with the initial linear field
using a mock galaxy sample that is designed to mimic the clustering of the BOSS
CMASS galaxies. The results directly provide the BAO damping as a function of
wavenumber that can be implemented into the Fisher matrix analysis. We focus on
investigating the dependence of the propagator on a choice of smoothing filters
and on two major different conventions of the redshift-space density field
reconstruction that have been used in literature. By estimating the BAO
signal-to-noise for each case, we predict constraints on the angular diameter
distance and Hubble parameter using the Fisher matrix analysis. We thus
determine an optimal Gaussian smoothing filter scale for the signal-to-noise
level of the BOSS CMASS. We also present appropriate BAO fitting models for
different reconstruction methods based on the first and second order Lagrangian
perturbation theory in Fourier space. Using the mock data, we show that the
modified BAO fitting model can substantially improve the accuracy of the BAO
position in the best fits as well as the goodness of the fits. |
Effect of primordial non-Gaussianities on the far-UV luminosity function
of high-redshift galaxies: implications for cosmic reionization: [Abridged] Understanding how the intergalactic medium (IGM) was reionized at
z > 6 is one of the big challenges of current high redshift astronomy. It
requires modelling the collapse of the first astrophysical objects (Pop III
stars, first galaxies) and their interaction with the IGM, while at the same
time pushing current observational facilities to their limits. The
observational and theoretical progress of the last few years have led to the
emergence of a coherent picture in which the budget of hydrogen-ionizing
photons is dominated by low-mass star-forming galaxies, with little
contribution from Pop III stars and quasars. The reionization history of the
Universe therefore critically depends on the number density of low-mass
galaxies at high redshift. In this work, we explore how changes in the
statistical properties of initial density fluctuations affect the formation of
early galaxies. Following Habouzit et al. (2014), we run 5 N-body simulations
with Gaussian and (scale-dependent) non-Gaussian initial conditions, all
consistent with Planck constraints. By appealing to a galaxy formation model
and to a population synthesis code, we compute the far-UV galaxy luminosity
function down to M_UV = -14 at redshift 7 < z < 15. We find that models with
strong primordial non-Gaussianities on < Mpc scales show a far-UV luminosity
function significantly enhanced in low-mass galaxies. We adopt a reionization
model calibrated from state-of-the-art hydrodynamical simulations and show that
such non-Gaussianities leave a clear imprint on the Universe reionization
history and electron Thomson scattering optical depth tau_E. Although current
uncertainties in the physics of reionization and on the determination of tau_E
still dominate the signatures of non-Gaussianities, our results suggest that
tau_E could ultimately be used to constrain the statistical properties of
initial density fluctuations. | Noiseless Gravitational Lensing Simulations: The microphysical properties of the DM particle can, in principle, be
constrained by the properties and abundance of substructures in DM halos, as
measured through strong gravitational lensing. Unfortunately, there is a lack
of accurate theoretical predictions for the lensing signal of substructures,
mainly because of the discreteness noise inherent to N-body simulations. Here
we present Recursive-TCM, a method that is able to provide lensing predictions
with an arbitrarily low discreteness noise, without any free parameters or
smoothing scale. This solution is based on a novel way of interpreting the
results of N-body simulations, where particles simply trace the evolution and
distortion of Lagrangian phase-space volume elements. We discuss the advantages
of this method over the widely used cloud-in-cells and adaptive-kernel
smoothing density estimators. Applying the new method to a cluster-sized DM
halo simulated in warm and cold DM scenarios, we show how the expected
differences in their substructure population translate into differences in the
convergence and magnification maps. We anticipate that our method will provide
the high-precision theoretical predictions required to interpret and fully
exploit strong gravitational lensing observations. |
A 21-cm power spectrum at 48 MHz, using the Owens Valley Long Wavelength
Array: The Large-aperture Experiment to detect the Dark Age (LEDA) was designed to
measure the 21-cm signal from neutral hydrogen at Cosmic Dawn, $z \approx
$15-30. Using observations made with the $\approx $ 200 m diameter core of the
Owens Valley Long Wavelength Array (OVRO-LWA), we present a 2-D cylindrical
spatial power spectrum for data at 43.1-53.5 MHz ($z_{\rm median}\approx 28$)
incoherently integrated for 4 hours, and an analysis of the array sensitivity.
Power from foregrounds is localized to a "wedge" within $k_\perp, k_\parallel$
space. After calibration of visibilities using 5 bright compact sources
including VirA, we measure $\Delta^2(k) \approx 2 \times 10^{12}\
\mathrm{mK}^2$ outside the foreground wedge, where an uncontaminated
cosmological signal would lie, in principle. The measured $\Delta^2(k)$ is an
upper limit that reflects a combination of thermal instrumental and sky noise,
and unmodelled systematics that scatter power from the wedge, as will be
discussed. By differencing calibrated visibilities for close pairs of frequency
channels, we suppress foreground sky structure and systematics, extract thermal
noise, and use a mix of coherent and incoherent integration to simulate a
noise-dominated power spectrum for a 3000 h observation and $z = $16-37. For
suitable calibration quality, the resulting noise level, $\Delta^2(k) \approx
100$ mK$^2$ (k = 0.3 Mpc$^{-1}$), would be sufficient to detect peaks in the
21-cm spatial power spectrum due to early Ly-$\alpha$ and X-ray sources, as
predicted for a range of theoretical model parameters. | The thermal history of the intergalactic medium at $3.9 \leq z \leq 4.3$: A new determination of the temperature of the intergalactic medium over $3.9
\leq z \leq 4.3$ is presented. We applied the curvature method on a sample of
10 high resolution quasar spectra from the Ultraviolet and Visual Echelle
Spectrograph on the VLT/ESO. We measured the temperature at mean density by
determining the temperature at the characteristic overdensity, which is tight
function of the absolute curvature irrespective of $\gamma$. Under the
assumption of fiducial value of $\gamma = 1.4$, we determined the values of
temperatures at mean density $T_{0} = 7893^{+1417}_{-1226}$ K and $T_{0} =
8153^{+1224}_{-993}$ K for redshift range of $3.9 \leq z \leq 4.1$ and $4.1
\leq z \leq 4.3$, respectively. Even though the results show no strong
temperature evolution over the studied redshift range, our measurements are
consistent with an intergalactic medium thermal history that includes a
contribution from He II reionization. |
Probing ionizing radiation of L<~0.1L* star-forming galaxies at z>~3
with strong lensing: We show the effectiveness of strong lensing in the characterisation of Lyman
continuum emission from faint L<~0.1L* star-forming galaxies at redshift >~ 3.
Past observations of L>~L* galaxies at redshift >~3 have provided upper limits
of the average escape fraction of ionising radiation of fesc~5%. Galaxies with
relatively high fesc (>10%) seem to be particularly rare at these luminosities,
there is therefore the need to explore fainter limits. Before the advent of
giant ground based telescopes, one viable way to probe fesc down to 0.05-0.15L*
is to exploit strong lensing magnification. This is investigated with Monte
Carlo simulations that take into account the current observational
capabilities. Adopting a lensing cross-section of 10 arcmin^2 within which the
magnification is higher than 1 (achievable with about 4-5 galaxy clusters),
with a U-band survey depth of 30(30.5) (AB, 1-sigma), it is possible to
constrain fesc for z~3 star-forming galaxies down to 15(10)% at 3-sigma for
L<0.15L* luminosities. This is particularly interesting if fesc increases at
fainter luminosities, as predicted from various HI reionization scenarios and
radiation transfer modelling. Ongoing observational programs on galaxy clusters
are discussed and offer positive prospects for the future, even though from
space the HST/WFC3 instrument represents the only option we have to investigate
details of the spatial distribution of the Lyman continuum emission arising
from z~2-4 galaxies. | Observed Scaling Relations for Strong Lensing Clusters: Consequences for
Cosmology and Cluster Assembly: Scaling relations of observed galaxy cluster properties are useful tools for
constraining cosmological parameters as well as cluster formation histories.
One of the key cosmological parameters, sigma8, is constrained using observed
clusters of galaxies, although current estimates of sigma8 from the scaling
relations of dynamically relaxed galaxy clusters are limited by the large
scatter in the observed cluster mass-temperature (M-T) relation. With a sample
of eight strong lensing clusters at 0.3 < z <0.8, we find that the observed
cluster concentration-mass relation can be used to reduce the M-T scatter by a
factor of 6. Typically only relaxed clusters are used to estimate sigma8, but
combining the cluster concentration-mass relation with the M-T relation enables
the inclusion of unrelaxed clusters as well. Thus, the resultant gains in the
accuracy of sigma8 measurements from clusters are twofold: the errors on sigma8
are reduced and the cluster sample size is increased. Therefore, the statistics
on sigma8 determination from clusters are greatly improved by the inclusion of
unrelaxed clusters. Exploring cluster scaling relations further, we find that
the correlation between brightest cluster galaxy (BCG) luminosity and cluster
mass offers insight into the assembly histories of clusters. We find
preliminary evidence for a steeper BCG luminosity - cluster mass relation for
strong lensing clusters than the general cluster population, hinting that
strong lensing clusters may have had more active merging histories. |
Interaction between collisionless galactic discs and nonaxissymmetric
dark matter haloes: Using $N$-body simulations ($N\sim 10^6 - 10^7$), we examine how a
non-axisymmetric dark halo affects the dynamical evolution of the structure in
collisionless (stellar) discs. We demonstrate how the model parameters such as
mass of the halo, initial conditions in the disc and the halo axes ratio affect
morphology and kinematics of the stellar discs. We show that a non-axisymmetric
halo can generate a large-scale spiral density pattern in the embedded stellar
disc. The pattern is observed in the disc for many periods of its revolution,
even if the disc is gravitationally over-stable. The growth of the spiral arms
is not accompanied by significant dynamical heating of the disc, irrelevant to
its initial parameters. We also investigate transformation of the dark halo's
shape driven by the long-lived spiral pattern in the disc . We show that the
analysis of the velocity field in the stellar disc and in the spiral pattern
gives us a possibility to figure out the spatial orientation of the
triaxial-shaped dark halo and to measure the triaxiality. | A numerical model of resistive generation of intergalactic magnetic
field at cosmic dawn: Miniati and Bell (2011) proposed a mechanism for the generation of magnetic
seeds that is based the finite resistivity of the low temperature IGM in the
high redshift universe. In this model, cosmic-ray protons generated by the
first generation of galaxies, escape into the intergalactic medium carrying an
electric current that induces return currents, $j_t$, and associated electric
fields, $\vec E=\eta\vec j_t$ there. Because the resistivity, $\eta$, depends
on the IGM temperature, which is highly inhomogeneous due to adiabatic
contraction and shocks produced by structure formation, a non-vanishing curl of
the electric field exists which sustains the growth of magnetic field. In this
contribution we have developed an approximate numerical model for this process
by implementing the source terms of the resistive mechanism in the cosmological
code CHARM. Our numerical estimates substantiate the earlier analysis in
Miniati and Bell (2011) which found magnetic seeds between 10$^{-18}$ and
10$^{-16}$ Gauss throughout cosmic space at redshift z~6, consistent with
conservative estimates of magnetic fields in voids at z~0 from recent gamma-ray
experiments. |
Dark Energy Survey Year 1 Results: Methods for Cluster Cosmology and
Application to the SDSS: We perform the first blind analysis of cluster abundance data. Specifically,
we derive cosmological constraints from the abundance and weak-lensing signal
of \redmapper\ clusters of richness $\lambda\geq 20$ in the redshift range
$z\in[0.1,0.3]$ as measured in the Sloan Digital Sky Survey (SDSS). We
simultaneously fit for cosmological parameters and the richness--mass relation
of the clusters. For a flat $\Lambda$CDM cosmological model with massive
neutrinos, we find $S_8 \equiv
\sigma_{8}(\Omega_m/0.3)^{0.5}=0.79^{+0.05}_{-0.04}$. This value is both
consistent and competitive with that derived from cluster catalogues selected
in different wavelengths. Our result is also consistent with the combined
probes analyses by the Dark Energy Survey (DES) and the Kilo-Degree Survey
(KiDS), and with the Cosmic Microwave Background (CMB) anisotropies as measured
by \planck. We demonstrate that the cosmological posteriors are robust against
variation of the richness--mass relation model and to systematics associated
with the calibration of the selection function. In combination with Baryon
Acoustic Oscillation (BAO) data and Big-Bang Nucleosynthesis (BBN) data, we
constrain the Hubble rate to be $h=0.66\pm 0.02$, independent of the CMB.
Future work aimed at improving our understanding of the scatter of the
richness--mass relation has the potential to significantly improve the
precision of our cosmological posteriors. The methods described in this work
were developed for use in the forthcoming analysis of cluster abundances in the
DES. Our SDSS analysis constitutes the first part of a staged-unblinding
analysis of the full DES data set. | Early-type galaxies at z~1.3. II. Masses and ages of early-type galaxies
in different environments and their dependence on stellar population model
assumptions: We have derived masses and ages for 79 early-type galaxies (ETGs) in
different environments at z~1.3 in the Lynx supercluster and in the GOODS/CDF-S
field using multiwavelength (0.6-4.5 $\mu$m; KPNO, Palomar, Keck, HST, Spitzer)
datasets. At this redshift the contribution of the TP-AGB phase is important
for ETGs, and the mass and age estimates depend on the choice of the stellar
population model used in the spectral energy distribution fits. We describe in
detail the differences among model predictions for a large range of galaxy
ages, showing the dependence of these differences on age. Current models still
yield large uncertainties. While recent models from Maraston and Charlot &
Bruzual offer better modeling of the TP-AGB phase with respect to less recent
Bruzual & Charlot models, their predictions do not often match. The modeling of
this TP-AGB phase has a significant impact on the derived parameters for
galaxies observed at high-redshift. Some of our results do not depend on the
choice of the model: for all models, the most massive galaxies are the oldest
ones, independent of the environment. When using Maraston and Charlot & Bruzual
models, the mass distribution is similar in the clusters and in the groups,
whereas in our field sample there is a deficit of massive (M $\gtrsim$ 10^11
Msun) ETGs. According to those last models, ETGs belonging to the cluster
environment host on average older stars with respect to group and field
populations. This difference is less significant than the age difference in
galaxies of different masses. |
Formation rates of Dark Matter Haloes: We derive an estimate of the rate of formation of dark matter halos per unit
volume as a function of the halo mass and redshift of formation. Analytical
estimates of the number density of dark matter halos are useful in modeling
several cosmological phenomena. We use the excursion set formalism for
computing the formation rate of dark matter halos. We use an approach that
allows us to differentiate between major and minor mergers, as this is a
pertinent issue for semi-analytic models of galaxy formation. We compute the
formation rate for the Press-Schechter and the Sheth-Tormen mass function. We
show that the formation rate computed in this manner is positive at all scales.
We comment on the Sasaki formalism where negative halo formation rates are
obtained. Our estimates compare very well with N-Body simulations for a variety
of models. We also discuss the halo survival probability and the formation
redshift distributions using our method. | Exact nonlinear inhomogeneities in $Λ$CDM cosmology: At a time when galaxy surveys and other observations are reaching
unprecedented sky coverage and precision it seems timely to investigate the
effects of general relativistic nonlinear dynamics on the growth of structures
and on observations. Analytic inhomogeneous cosmological models are an
indispensable way of investigating and understanding these effects in a
simplified context.
In this paper, we develop exact inhomogeneous solutions of general relativity
with pressureless matter (dust, describing cold dark matter) and cosmological
constant $\Lambda$, which can be used to model an arbitrary initial matter
distribution along one line of sight. In particular, we consider the second
class Szekeres models with $\Lambda$ and split their dynamics into a flat
$\Lambda$CDM background and exact nonlinear inhomogeneities, obtaining several
new results. One single metric function $Z$ describes the deviation from the
background. We show that $F$, the time dependent part of $Z$, satisfies the
familiar linear differential equation for $\delta$, the first-order density
perturbation of dust, with the usual growing and decaying modes. In the limit
of small perturbations, $\delta \approx F$ as expected, and the growth of
inhomogeneities links up exactly with standard perturbation theory. We provide
analytic expressions for the exact nonlinear $\delta$ and the growth factor in
our models. For the case of over-densities, we find that, depending on the
initial conditions, the growing mode may or may not lead to a pancake
singularity, analogous to a Zel'dovich pancake. This is in contrast with the
$\Lambda=0$ pure Einstein-de-Sitter background where, at any given point in
comoving (Lagrangian) coordinates pancakes will always occur. |
The Kinematic Sunyaev-Zel'dovich Effect with Projected Fields: A Novel
Probe of the Baryon Distribution with Planck, WMAP, and WISE Data: The kinematic Sunyaev-Zel'dovich (kSZ) effect --- the Doppler boosting of
cosmic microwave background (CMB) photons due to Compton-scattering off free
electrons with non-zero bulk velocity --- probes the abundance and distribution
of baryons in the Universe. All kSZ measurements to date have explicitly
required spectroscopic redshifts. Here, we implement a novel estimator for the
kSZ -- large-scale structure cross-correlation based on projected fields: it
does not require redshift estimates for individual objects, allowing kSZ
measurements from large-scale imaging surveys. We apply this estimator to
cleaned CMB temperature maps constructed from Planck and Wilkinson Microwave
Anisotropy Probe data and a galaxy sample from the Wide-field Infrared Survey
Explorer (WISE). We measure the kSZ effect at 3.8-4.5$\sigma$ significance,
depending on the use of additional WISE galaxy bias constraints. We verify that
our measurements are robust to possible dust emission from the WISE galaxies.
Assuming the standard $\Lambda$CDM cosmology, we directly constrain $(
{f_{b}}/{0.158} ) ( {f_{\rm free}}/{1.0} ) = 1.48 \pm 0.19$ (statistical error
only) at redshift $z \approx 0.4$, where $f_{b}$ is the fraction of matter in
baryonic form and $f_{\rm free}$ is the free electron fraction. This is the
tightest kSZ-derived constraint reported to date on these parameters. The
consistency between the $f_{b}$ value found here and the values inferred from
analyses of the primordial CMB and Big Bang nucleosynthesis verifies that
baryons approximately trace the dark matter distribution down to $\sim$Mpc
scales. While our projected-field estimator is already competitive with other
kSZ approaches when applied to current datasets (because we are able to use the
full-sky WISE photometric survey), it will yield enormous signal-to-noise when
applied to upcoming high-resolution, multi-frequency CMB surveys. | 2MASS photometry and age estimate of globular clusters in the outer halo
of M31: We present the first photometric results in J, H, and K_s from 2MASS imaging
of 10 classical globular clusters in the far outer regions of M31. Combined
with the V and I photometric data from previous literature, we constructed the
color-color diagram between J-K_s and V-I. By comparing the integrated
photometric measurements with evolutionary models, we estimate the ages of
these clusters. The results showed that, all of these clusters are older than
$3\times 10^9$ yrs, of which 4 are older than 10 Gyrs and the other 6 are in
intermediate ages between 3-8 Gyrs. The masses for these outer halo GCs are
from $7.0\times 10^4 M_sun$ to $1.02\times 10^6 M_sun$. We argued that, GC2 and
GC3, the ages, metallicities and the distance moduli of which are nearly the
same, were accreted from the same satellite galaxy, if they did not form {\it
in situ}. The statistical results show that, ages and metallicities for these
10 M31 outer halo GCs do not vary with projected radial position, and the
relationship between age and metallicity doest not exit. |
On the Spin Bias of Satellite Galaxies in the Local Group-like
Environment: We utilize the Millennium-II simulation databases to study the spin bias of
dark subhalos in the Local Group-like systems which have two prominent
satellites with comparable masses. Selecting the group-size halos with total
mass similar to that of the Local Group (LG) from the friends-of-friends halo
catalog and locating their subhalos from the substructure catalog, we determine
the most massive (main) and second to the most massive (submain) ones among the
subhalos hosted by each selected halo. When the dimensionless spin parameter
(lambda) of each subhalo is derived from its specific angular momentum and
circular velocity at virial radius, a signal of correlation is detected between
the spin parameters of the subhalos and the main-to-submain mass ratios of
their host halos at z=0: The higher main-to-submain mass ratio a host halo has,
the higher mean spin parameter its subhalos have. It is also found that the
correlations exist even for the subhalo progenitors at z=0.5 and z=1. Our
interpretation of this result is that the subhalo spin bias is not a transient
effect but an intrinsic property of a LG-like system with higher main-to-
submain mass ratio, caused by stronger anisotropic stress in the region. A
cosmological implication of our result is also discussed. | Fossil Groups Origins: I. RX J105453.3+552102 a very massive and relaxed
system at z~0.5: The most accepted scenario for the origin of fossil groups (FGs) is that they
are galaxy associations in which the merging rate was fast and efficient. These
systems have assembled half of their mass at early epoch of the Universe,
subsequently growing by minor mergers. They could contain a fossil record of
the galaxy structure formation. We have started a project in order to
characterize a large sample of FGs. In this paper we present the analysis of
the fossil system RX J105453.3+552102. Optical deep images were used for
studying the properties of the brightest group galaxy and for computing the
photometric luminosity function of the group. We have also performed a detail
dynamical analysis of the system based on redshift data for 116 galaxies. This
galaxy system is located at z=0.47, and shows a quite large line-of-sight
velocity dispersion \sigma_{v}~1000 km/s. Assuming the dynamical equilibrium,
we estimated a virial mass of M ~ 10^{15} h_{70} M_{\odot}. No evidence of
substructure was found within 1.4 Mpc radius. We found a statistically
significant departure from Gaussianity of the group members velocities in the
most external regions of the group. This could indicate the presence of
galaxies in radial orbits in the external region of the group. We also found
that the photometrical luminosity function is bimodal, showing a lack of M_{r}
~ -19.5 galaxies. The brightest group galaxy shows low Sersic parameter (n~2)
and a small peculiar velocity. Indeed, our accurate photometry shows that the
difference between the brightest and the second brightest galaxies is 1.9 mag
in the r-band, while the classical definition of FGs is based on a magnitude
gap of 2. We conclude that this fossil system does not follow the empirical
definition of FGs. Nevertheless, it is a massive, old and undisturbed galaxy
system with little infall of L^{*} galaxies since its initial collapse. |
Aspects of Dark Matter Annihilation in Cosmology: Cosmic microwave background (CMB) constraints on dark matter annihilation are
a uniquely powerful tool in the quest to understand the nature of dark matter.
Annihilation of dark matter to Standard Model particles between recombination
and reionization heats baryons, ionizes neutral hydrogen, and alters the CMB
visibility function. Surprisingly, CMB bounds on dark matter annihilation are
not expected to improve significantly with the dramatic improvements in
sensitivity expected in future cosmological surveys. In this paper, we will
present a simple physical description of the origin of the CMB constraints and
explain why they are nearly saturated by current observations. The essential
feature is that dark matter annihilation primarily affects the ionization
fraction which can only increase substantially at times when the universe was
neutral. The resulting change to the CMB occurs on large angular scales and
leads to a phenomenology similar to that of the optical depth to reionization.
We will demonstrate this impact on the CMB both analytically and numerically.
Finally, we will discuss the additional impact that changing the ionization
fraction has on large scale structure. | The insignificance of major mergers in driving star formation at z~2: We study the significance of major-merger-driven star formation in the early
Universe, by quantifying the contribution of this process to the total star
formation budget in 80 massive (M* > 10^10 MSun) galaxies at z~2. Employing
visually-classified morphologies from rest-frame V-band HST imaging, we find
that 55+/-14% of the star formation budget is hosted by non-interacting
late-types, with 27+/-8% in major mergers and 18+/-6% in spheroids. Given that
a system undergoing a major merger continues to experience star formation
driven by other processes at this epoch (e.g. cold accretion, minor mergers),
~27% is an upper limit to the major-merger contribution to star formation
activity at this epoch. The ratio of the average specific star formation rate
in major mergers to that in the non-interacting late-types is ~2.2:1,
suggesting that the enhancement of star formation due to major merging is
typically modest, and that just under half the star formation in systems
experiencing major mergers is unrelated to the merger itself. Taking this into
account, we estimate that the actual major-merger contribution to the star
formation budget may be as low as ~15%. While our study does not preclude a
major-merger-dominated era in the very early Universe, if the major-merger
contribution to star formation does not evolve strongly into larger look-back
times, then this process has a relatively insignificant role in driving stellar
mass assembly over cosmic time. |
Star formation efficiency in the Barred Spiral Galaxy NGC 4303: We present new $^{12}$CO(J=1-0) observations of the barred galaxy NGC 4303
using the Nobeyama 45m telescope (NRO45) and the Combined Array for Research in
Millimeter-wave Astronomy (CARMA). The H$\alpha$ images of barred spiral
galaxies often show active star formation in spiral arms, but less so in bars.
We quantify the difference by measuring star formation rate and efficiency at a
scale where local star formation is spatially resolved. Our CO map covers the
central 2$\farcm$3 region of the galaxy; the combination of NRO45 and CARMA
provides a high fidelity image, enabling accurate measurements of molecular gas
surface density. We find that star formation rate and efficiency are twice as
high in the spiral arms as in the bar. We discuss this difference in the
context of the Kennicutt-Schimidt (KS) law, which indicates a constant star
formation rate at a given gas surface density. The KS law breaks down at our
native resolution ($\sim$ 250 pc), and substantial smoothing (to 500 pc) is
necessary to reproduce the KS law, although with greater scatter. | The Progenitor of Supernova 2011dh/PTF11eon in Messier 51: We have identified a luminous star at the position of supernova (SN)
2011dh/PTF11eon, in pre-SN archival, multi-band images of the nearby, nearly
face-on galaxy Messier 51 (M51) obtained by the Hubble Space Telescope with the
Advanced Camera for Surveys. This identification has been confirmed, to the
highest available astrometric precision, using a Keck-II adaptive-optics image.
The available early-time spectra and photometry indicate that the SN is a
stripped-envelope, core-collapse Type IIb, with a more compact progenitor
(radius ~1e11 cm) than was the case for the well-studied SN IIb 1993J. We infer
that the extinction to SN 2011dh and its progenitor arises from a low Galactic
foreground contribution, and that the SN environment is of roughly solar
metallicity. The detected object has absolute magnitude M_V^0 ~ -7.7 and
effective temperature ~6000 K. The star's radius, ~1e13 cm, is more extended
than what has been inferred for the SN progenitor. We speculate that the
detected star is either an unrelated star very near the position of the actual
progenitor, or, more likely, the progenitor's companion in a mass-transfer
binary system. The position of the detected star in a Hertzsprung-Russell
diagram is consistent with an initial mass of 17--19 Msun. The light of this
star could easily conceal, even in the ultraviolet, the presence of a stripped,
compact, very hot (~1e5 K), nitrogen-rich Wolf-Rayet star progenitor. |
Sensitivity of galaxy cluster dark energy constraints to halo modeling
uncertainties: We perform a sensitivity study of dark energy constraints from galaxy cluster
surveys to uncertainties in the halo mass function, bias and the
mass-observable relation. For a set of idealized surveys, we evaluate
cosmological constraints as priors on sixteen nuisance parameters in the halo
modeling are varied. We find that surveys with a higher mass limit are more
sensitive to mass-observable uncertainties while surveys with low mass limits
that probe more of the mass function shape and evolution are more sensitive to
mass function errors. We examine the correlations among nuisance and
cosmological parameters. Mass function parameters are strongly positively
(negatively) correlated with Omega_DE (w). For the mass-observable parameters,
Omega_DE is most sensitive to the normalization and its redshift evolution
while w is more sensitive to redshift evolution in the variance. While survey
performance is limited mainly by mass-observable uncertainties, the current
level of mass function error is responsible for up to a factor of two
degradation in ideal cosmological constraints. For surveys that probe to low
masses (10^13.5 h^-1 M_sun), even percent-level constraints on model nuisance
parameters result in a degradation of ~ sqrt{2} (2) on Omega_DE (w) relative to
perfect knowledge. | Redshift Drift in LTB Void Universes: We study the redshift drift, i.e., the time derivative of the cosmological
redshift in the Lema\^itre-Tolman-Bondi (LTB) solution in which the observer is
assumed to be located at the symmetry center. This solution has often been
studied as an anti-Copernican universe model to explain the acceleration of
cosmic volume expansion without introducing the concept of dark energy. One of
decisive differences between LTB universe models and Copernican universe models
with dark energy is believed to be the redshift drift. The redshift drift is
negative in all known LTB universe models, whereas it is positive in the
redshift domain $z \lesssim 2$ in Copernican models with dark energy. However,
there have been no detailed studies on this subject. In the present paper, we
prove that the redshift drift of an off-center source is always negative in the
case of LTB void models. We also show that the redshift drift can be positive
with an extremely large hump-type inhomogeneity. Our results suggest that we
can determine whether we live near the center of a large void without dark
energy by observing the redshift drift. |
Toward a Measurement of the Transverse Peculiar Velocity of Galaxy Pairs: The transverse peculiar velocities caused by the mass distribution of
large-scale structure provide a test of the theoretical matter power spectrum
and the cosmological parameters that contribute to its shape. Typically, the
matter density distribution of the nearby Universe is measured through redshift
or line-of-sight peculiar velocity surveys. However, both methods require
model-dependent distance measures to place the galaxies or to differentiate
peculiar velocity from the Hubble expansion. In this paper, we use the
correlated proper motions of galaxy pairs from the VLBA Extragalactic Proper
Motion Catalog to place limits on the transverse peculiar velocity of galaxy
pairs with comoving separations <1500 Mpc without a reliance on precise
distance measurements. The relative proper motions of galaxy pairs across the
line of sight can be directly translated into relative peculiar velocities
because no proper motion will occur in a homogeneous expansion. We place a 3
sigma limit on the relative proper motion of pairs with comoving separations <
100 Mpc of -17.4 microas/yr < thetadot / sin theta < 19.8 microas/yr. We also
confirm that large-separation objects (> 200 Mpc) are consistent with pure
Hubble expansion to within ~ 5.3 microas/yr (1 sigma). Finally, we predict that
Gaia end-of-mission proper motions will be able to significantly detect the
mass distribution of large-scale structure on length scales < 25 Mpc. This
future detection will allow a test of the shape of the theoretical mass power
spectrum without a reliance on precise distance measurements. | A Bayesian method for combining theoretical and simulated covariance
matrices for large-scale structure surveys: Accurate and precise covariance matrices will be important in enabling
planned cosmological surveys to detect new physics. Standard methods imply
either the need for many N-body simulations in order to obtain an accurate
estimate, or a precise theoretical model. We combine these approaches by
constructing a likelihood function conditioned on simulated and theoretical
covariances, consistently propagating noise from the finite number of
simulations and uncertainty in the theoretical model itself using an
informative Inverse-Wishart prior. Unlike standard methods, our approach allows
the required number of simulations to be less than the number of summary
statistics. We recover the linear 'shrinkage' covariance estimator in the
context of a Bayesian data model, and test our marginal likelihood on simulated
mock power spectrum estimates. We conduct a thorough investigation into the
impact of prior confidence in different choices of covariance models on the
quality of model fits and parameter variances. In a simplified setting we find
that the number of simulations required can be reduced if one is willing to
accept a mild degradation in the quality of model fits, finding that even
weakly informative priors can help to reduce the simulation requirements. We
identify the correlation matrix of the summary statistics as a key quantity
requiring careful modelling. Our approach can be easily generalized to any
covariance model or set of summary statistics, and elucidates the role of
hybrid estimators in cosmological inference. |
TDCOSMO IV: Hierarchical time-delay cosmography -- joint inference of
the Hubble constant and galaxy density profiles: The H0LiCOW collaboration inferred via gravitational lensing time delays a
Hubble constant $H_0=73.3^{+1.7}_{-1.8}$ km s$^{-1}{\rm Mpc}^{-1}$, describing
deflector mass density profiles by either a power-law or stars plus standard
dark matter halos. The mass-sheet transform (MST) that leaves the lensing
observables unchanged is considered the dominant source of residual uncertainty
in $H_0$. We quantify any potential effect of the MST with flexible mass models
that are maximally degenerate with H0. Our calculation is based on a new
hierarchical approach in which the MST is only constrained by stellar
kinematics. The approach is validated on hydrodynamically simulated lenses. We
apply the method to the TDCOSMO sample of 7 lenses (6 from H0LiCOW) and measure
$H_0=74.5^{+5.6}_{-6.1}$ km s$^{-1}{\rm Mpc}^{-1}$. In order to further
constrain the deflector mass profiles, we then add imaging and spectroscopy for
33 strong gravitational lenses from the SLACS sample. For 9 of the SLAC lenses
we use resolved kinematics to constrain the stellar anisotropy. From the joint
analysis of the TDCOSMO+SLACS sample, we measure $H_0=67.4^{+4.1}_{-3.2}$ km
s$^{-1}{\rm Mpc}^{-1}$, assuming that the TDCOSMO and SLACS galaxies are drawn
from the same parent population. The blind H0LiCOW, TDCOSMO-only and
TDCOSMO+SLACS analyses are in mutual statistical agreement. The TDCOSMO+SLACS
analysis prefers marginally shallower mass profiles than H0LiCOW or
TDCOSMO-only. While our new analysis does not statistically invalidate the mass
profile assumptions by H0LiCOW, and thus their $H_0$ measurement relying on
those, it demonstrates the importance of understanding the mass density profile
of elliptical galaxies. The uncertainties on $H_0$ derived in this paper can be
reduced by physical or observational priors on the form of the mass profile, or
by additional data, chiefly spatially resolved kinematics of lens galaxies. | Astrophysical Distance Scale IV. Preliminary Zero-Point Calibration of
the JAGB Method in the HST/WFC3-IR Broad J-Band (F110W) Filter: We present an absolute calibration of the J-region Asymptotic Giant Branch
(JAGB) method using published photometry of resolved stars in 20 nearby
galaxies observed with HST using the WFC3-IR camera and the F110W (Broad
J-Band) filter. True distance moduli for each of the galaxies are based on the
Tip of the Red Giant Branch (TRGB) method as uniformly determined by Dalcanton
et al. (2012). From a composite color-magnitude diagram composed of over 6
million stars, leading to a sample of 453 JAGB stars in these galaxies, we find
M_{F110W}{JAGB} = -5.77 +/- 0.02 mag(statistical error on the mean). The
external scatter seen in a comparison of the individual TRGB and the JAGB
moduli is +/-0.081 mag (or 4% in distance). Some of this scatter can be
attributed to small-number statistics arising from the sparse JAGB populations
found in the generally low-luminosity galaxies that comprise the particular
sample studied here. However, if this inter-method scatter is shared equitably
between the JAGB and TRGB methods that implies that each are good to +/-0.06
mag, or better than 3% in distance. |
Resummed Perturbation Theory of Galaxy Clustering: The relationship between observed tracers such as galaxies and the underlying
dark matter distribution is crucial in extracting cosmological information. As
the linear bias model breaks down at quasi-linear scales, the standard
perturbative approach of the nonlinear Eulerian bias model (EBM) is not
accurate enough in describing galaxy clustering. In this paper, we discuss such
a model in the context of resummed perturbation theory, and further generalize
it to incorporate the subsequent gravitational evolution by combining with a
Lagrangian description of galaxies' motion. The multipoint propagators we
constructed for such model also exhibit exponential damping similar to their
dark matter counterparts, therefore the convergence property of statistics
built upon these quantities is improved. This is achieved by applying both
Eulerian and Lagrangian resummation techniques of dark matter field developed
in recent years. As inherited from the Lagrangian description of galaxy density
evolution, our approach automatically incorporates the non-locality induced by
gravitational evolution after the formation of the tracer, and also allows us
to include a continuous galaxy formation history by temporally
weighted-averaging relevant quantities with the galaxy formation rate. | CSST WL preparation I: forecast the impact from non-Gaussian covariances
and requirements on systematics-control: The precise estimation of the statistical errors and accurate removal of the
systematical errors are the two major challenges for the stage IV cosmic shear
surveys. We explore their impact for the China Space-Station Telescope (CSST)
with survey area $\sim17,500\deg^2$ up to redshift $\sim4$. We consider
statistical error contributed from Gaussian covariance, connected non-Gaussian
covariance and super-sample covariance. We find the non-Gaussian covariances,
which is dominated by the super-sample covariance, can largely reduce the
signal-to-noise of the two-point statistics for CSST, leading to a $\sim1/3$
loss in the figure-of-merit for the matter clustering properties
($\sigma_8-\Omega_m$ plane) and $1/6$ in the dark energy equation-of-state
($w_0-w_a$ plane). We further put requirements of systematics-mitigation on:
intrinsic alignment of galaxies, baryonic feedback, shear multiplicative bias,
and bias in the redshift distribution, for an unbiased cosmology. The $10^{-2}$
to $10^{-3}$ level requirements emphasize strong needs in related studies, to
support future model selections and the associated priors for the nuisance
parameters. |
Phenomenology of dark energy: general features of large-scale
perturbations: We present a systematic exploration of dark energy and modified gravity
models containing a single scalar field non-minimally coupled to the metric.
Even though the parameter space is large, by exploiting an effective field
theory (EFT) formulation and by imposing simple physical constraints such as
stability conditions and (sub-)luminal propagation of perturbations, we arrive
at a number of generic predictions. (1) The linear growth rate of matter
density fluctuations is generally suppressed compared to $\Lambda$CDM at
intermediate redshifts ($0.5 \lesssim z \lesssim 1$), despite the introduction
of an attractive long-range scalar force. This is due to the fact that, in
self-accelerating models, the background gravitational coupling weakens at
intermediate redshifts, over-compensating the effect of the attractive scalar
force. (2) At higher redshifts, the opposite happens; we identify a period of
super-growth when the linear growth rate is larger than that predicted by
$\Lambda$CDM. (3) The gravitational slip parameter $\eta$ - the ratio of the
space part of the metric perturbation to the time part - is bounded from above.
For Brans-Dicke-type theories $\eta$ is at most unity. For more general
theories, $\eta$ can exceed unity at intermediate redshifts, but not more than
about $1.5$ if, at the same time, the linear growth rate is to be compatible
with current observational constraints. We caution against phenomenological
parametrization of data that do not correspond to predictions from viable
physical theories. We advocate the EFT approach as a way to constrain new
physics from future large-scale-structure data. | Stability of cosmological detonation fronts: The steady state propagation of a phase transition front is classified,
according to hydrodynamics, as a deflagration or a detonation, depending on its
velocity with respect to the fluid. These propagation modes are further divided
into three types, namely, weak, Jouguet, and strong solutions, according to
their disturbance of the fluid. However, some of these hydrodynamic modes will
not be realized in a phase transition. One particular cause is the presence of
instabilities. In this work we study the linear stability of weak detonations,
which are generally believed to be stable. After discussing in detail the weak
detonation solution, we consider small perturbations of the interface and the
fluid configuration. When the balance between the driving and friction forces
is taken into account, it turns out that there are actually two different kinds
of weak detonations, which behave very differently as functions of the
parameters. We show that the branch of stronger weak detonations are unstable,
except very close to the Jouguet point, where our approach breaks down. |
Mind the gap: the power of combining photometric surveys with intensity
mapping: The long wavelength modes lost to bright foregrounds in the interferometric
21-cm surveys can partially be recovered using a forward modeling approach that
exploits the non-linear coupling between small and large scales induced by
gravitational evolution. In this work, we build upon this approach by
considering how adding external galaxy distribution data can help to fill in
these modes. We consider supplementing the 21-cm data at two different
redshifts with a spectroscopic sample (good radial resolution but low number
density) loosely modeled on DESI-ELG at $z=1$ and a photometric sample (high
number density but poor radial resolution) similar to LSST sample at $z=1$ and
$z=4$ respectively. We find that both the galaxy samples are able to
reconstruct the largest modes better than only using 21-cm data, with the
spectroscopic sample performing significantly better than the photometric
sample despite much lower number density. We demonstrate the synergies between
surveys by showing that the primordial initial density field is reconstructed
better with the combination of surveys than using either of them individually.
Methodologically, we also explore the importance of smoothing the density field
when using bias models to forward model these tracers for reconstruction. | Combining galaxy and 21cm surveys: Acoustic waves traveling through the early Universe imprint a characteristic
scale in the clustering of galaxies, QSOs and inter-galactic gas. This scale
can be used as a standard ruler to map the expansion history of the Universe, a
technique known as Baryon Acoustic Oscillations (BAO). BAO offer a
high-precision, low-systematics means of constraining our cosmological model.
The statistical power of BAO measurements can be improved if the `smearing' of
the acoustic feature by non-linear structure formation is undone in a process
known as reconstruction. In this paper we use low-order Lagrangian perturbation
theory to study the ability of $21\,$cm experiments to perform reconstruction
and how augmenting these surveys with galaxy redshift surveys at relatively low
number densities can improve performance. We find that the critical number
density which must be achieved in order to benefit $21\,$cm surveys is set by
the linear theory power spectrum near its peak, and corresponds to densities
achievable by upcoming surveys of emission line galaxies such as eBOSS and
DESI. As part of this work we analyze reconstruction within the framework of
Lagrangian perturbation theory with local Lagrangian bias, redshift-space
distortions, ${\bf k}$-dependent noise and anisotropic filtering schemes. |
Stochastic inflationary dynamics beyond slow-roll and consequences for
primordial black hole formation: We consider the impact of quantum diffusion on inflationary dynamics during
an ultra-slow-roll phase, which can be of particular significance for the
formation of primordial black holes. We show, by means of a fully analytical
approach, that the power spectrum of comoving curvature perturbations computed
in stochastic inflation matches precisely, at the linear level, the result
obtained by solving the Mukhanov-Sasaki equation, even in the presence of an
ultra-slow-roll phase. We confirm this result numerically in a model in which
the inflaton has a polynomial potential and is coupled quadratically to the
Ricci scalar. En route, we assess the role that quantum noise plays in the
presence of an ultra-slow-roll phase, and clarify the issue of the
quantum-to-classical transition in this scenario. | Sunyaev-Zel'dovich anisotropy due to Primordial black holes: We investigate the Sunyaev-Zel'dovich (SZ) effect caused by primordial black
holes (PBHs) on the cosmic microwave background (CMB) temperature fluctuations.
The gas accreting on a PBH heats up by the release of the gravitational energy.
As a result, the heated gas in the vicinity of the PBH emits the UV and X-ray
photons. These photons can ionize and heat the intergalactic medium (IGM)
around the PBH. Assuming the simple model of these emitting photons, we compute
the profiles of the IGM ionization fraction and temperature around a PBH. Using
these profiles, we evaluate the Compton $y$-parameter created by the IGM gas
around a PBH. Finally, we estimate the CMB temperature angular power spectrum
due to the PBH SZ effect in our model. We show that the SZ temperature
anisotropy due to the PBHs has the flat angular power spectrum on small scale,
$l\leq2000$ and could dominate the primordial temperature spectrum on smaller
scales than the Silk scale. This flat spectrum extends to the scale of the
ionized region by the PBH emission. We also discuss the impact of the
small-scale CMB measurement on the PBH abundance based on our results. |
A Bayesian Approach to Locating the Red Giant Branch Tip Magnitude (Part
I): We present a new approach for identifying the Tip of the Red Giant Branch
(TRGB) which, as we show, works robustly even on sparsely populated targets.
Moreover, the approach is highly adaptable to the available data for the
stellar population under study, with prior information readily incorporable
into the algorithm. The uncertainty in the derived distances is also made
tangible and easily calculable from posterior probability distributions. We
provide an outline of the development of the algorithm and present the results
of tests designed to characterize its capabilities and limitations. We then
apply the new algorithm to three M31 satellites: Andromeda I, Andromeda II and
the fainter Andromeda XXIII, using data from the Pan-Andromeda Archaeological
Survey (PAndAS), and derive their distances as $731^{(+ 5) + 18}_{(- 4) - 17}$
kpc, $634^{(+ 2) + 15}_{(- 2) - 14}$ kpc and $733^{(+ 13)+ 23}_{(- 11) - 22}$
kpc respectively, where the errors appearing in parentheses are the components
intrinsic to the method, while the larger values give the errors after
accounting for additional sources of error. These results agree well with the
best distance determinations in the literature and provide the smallest
uncertainties to date. This paper is an introduction to the workings and
capabilities of our new approach in its basic form, while a follow-up paper
shall make full use of the method's ability to incorporate priors and use the
resulting algorithm to systematically obtain distances to all of M31's
satellites identifiable in the PAndAS survey area. | Accounting for baryonic effects in cosmic shear tomography: Determining
a minimal set of nuisance parameters using PCA: Systematic uncertainties that have been subdominant in past large-scale
structure (LSS) surveys are likely to exceed statistical uncertainties of
current and future LSS data sets, potentially limiting the extraction of
cosmological information. Here we present a general framework (PCA
marginalization) to consistently incorporate systematic effects into a
likelihood analysis. This technique naturally accounts for degeneracies between
nuisance parameters and can substantially reduce the dimension of the parameter
space that needs to be sampled. As a practical application, we apply PCA
marginalization to account for baryonic physics as an uncertainty in cosmic
shear tomography. Specifically, we use CosmoLike to run simulated likelihood
analyses on three independent sets of numerical simulations, each covering a
wide range of baryonic scenarios differing in cooling, star formation, and
feedback mechanisms. We simulate a Stage III (Dark Energy Survey) and Stage IV
(Large Synoptic Survey Telescope/Euclid) survey and find a substantial bias in
cosmological constraints if baryonic physics is not accounted for. We then show
that PCA marginalization (employing at most 3 to 4 nuisance parameters) removes
this bias. Our study demonstrates that it is possible to obtain robust, precise
constraints on the dark energy equation of state even in the presence of large
levels of systematic uncertainty in astrophysical processes. We conclude that
the PCA marginalization technique is a powerful, general tool for addressing
many of the challenges facing the precision cosmology program. |
Constraints on the magnetic field in the inter-cluster bridge A399-A401: Galaxy cluster mergers are natural consequences of the structure formation in
the Universe. Such events involve a large amount of energy ($\sim 10^{63}$ erg)
dissipated during the process. Part of this energy can be channelled in
particle acceleration and magnetic field amplification, enhancing non-thermal
emission of the intra- and inter-cluster environment. Recently, low-frequency
observations have detected a bridge of diffuse synchrotron emission connecting
two merging galaxy clusters, Abell 399 and Abell 401. Such a result provides
clear observational evidence of relativistic particles and magnetic fields
in-between clusters. In this work, we have used LOw Frequency ARray (LOFAR)
observations at 144 MHz to study for the first time the polarized emission in
the A399-A401 bridge region. No polarized emission was detected from the bridge
region. Assuming a model where polarization is generated by multiple shocks,
depolarization can be due to Faraday dispersion in the foreground medium with
respect to the shocks. We constrained its Faraday dispersion to be greater than
0.10 rad m$^{-2}$ at 95% confidence level, which corresponds to an average
magnetic field of the bridge region greater than 0.46 nG (or 0.41 nG if we
include regions of the Faraday spectrum that are contaminated by Galactic
emission). This result is largely consistent with the predictions from
numerical simulations for Mpc regions where the gas density is $\sim 300$ times
larger than the mean gas density. | Cosmological dynamics and observational constraints on a viable $f(Q)$
non-metric gravity model: Inspired by an exponential $f(R)$ gravity model studied in the literature, in
this work we introduce a new and viable $f(Q)$ gravity model, which can be
represented as a perturbation of $\Lambda$CDM. Typically, within the realm of
$f(Q)$ gravity, the customary approach to investigate cosmological evolution
involves employing a parametrization of the Hubble expansion rate in terms of
the redshift, $H(z)$, among other strategies. In this work we have implemented
a different strategy, deriving an analytical approximation for $H(z)$, from
which we deduce approximated analytical expressions for the parameters
$w_{\rm{DE}}$, $w_{\rm{eff}}$, and $\Omega_{\rm{DE}}$, as well as the
deceleration parameter $q$. In order to verify the viability of this
approximate analytical solution, we examined the behavior of the these
parameters in the late-time regime\textbf, in terms of the free parameter of
the model, $b$. We find that for $b>0$, $w_{\rm{DE}}$ shows a quintessence-like
behavior, while for $b<0$, it shows a phantom-like behavior. However,
regardless of the sign of $b$, $w_{\rm{eff}}$ exhibits a quintessence-like
behavior. Furthermore, it has been deduced that as the magnitude of the
parameter $b$ increases, the present model deviates progressively from
$\Lambda$CDM. We have also performed a Markov Chain Monte Carlo statistical
analysis to test the model predictions with the Hubble parameter, the Pantheon
supernova (SN) observational data, and the combination of those samples,
obtaining constraints on the parameters of the model and the current values of
the Hubble parameter and the matter density. Our findings indicate that this
$f(Q)$ gravity model is indeed a viable candidate for describing the late-time
evolution of the Universe at the background level. |
The Central PNe Populations of External Galaxies with SAURON: Thanks to SAURON integral-field observations we uncovered the Planetary
Nebulae (PNe) populations inhabiting the central and nuclear regions of our
galactic neighbours M32 and M31, respectively, and discuss the significant
differences between their corresponding PNe luminosity functions in light of
the properties of their parent stellar populations. In particular, we conclude
that the lack of bright PNe in the nuclear regions of M31 is likely linked to
the nearly Solar value for the stellar metallicity, consistent with previous
suggestions that a larger metallicity would bias the Horizontal-Branch (HB)
populations toward bluer colors, with fewer red HB stars capable of producing
PNe and more blue HB stars that instead could contribute to the far-UV flux
that is observed in metal-rich early-type galaxies and, incidentally, also in
the nucleus of M31. | Coming of Age of the Standard Model: Cosmology now has a standard model - a remarkably simple description of the
universe, its contents and its history. A symposium held last September in
Cambridge, UK, gave this model a 'health check' and discussed fascinating
questions that lie beyond it. |
The spatial and velocity bias of linear density peaks and proto-haloes
in the Lambda cold dark matter cosmology: We use high resolution N-body simulations to investigate the Lagrangian bias
of cold dark matter haloes within the LCDM cosmology. Our analysis focuses on
"proto-haloes", which we identify in the simulation initial conditions with the
subsets of particles belonging to individual redshift-zero haloes. We then
calculate the number-density and velocity-divergence fields of proto-haloes and
estimate their auto spectral densities. We also measure the corresponding cross
spectral densities with the linear matter distribution. We use our results to
test a Lagrangian-bias model presented by Desjacques and Sheth which is based
on the assumption that haloes form out of local density maxima of a specific
height. Our comparison validates the predicted functional form for the
scale-dependence of the bias for both the density and velocity fields. We also
show that the bias coefficients are accurately predicted for the velocity
divergence. On the contrary, the theoretical values for the density bias
parameters do not accurately match the numerical results as a function of halo
mass. This is likely due to the simplistic assumptions that relate virialized
haloes to density peaks of a given height in the model. We also detect
appreciable stochasticity for the Lagrangian density bias, even on very large
scales. These are not included in the model at leading order but correspond to
higher order corrections. | Simulating Calibration and Beam Systematics for a Future CMB Space
Mission with the TOAST Package: We address in this work the instrumental systematic errors that can
potentially affect the forthcoming and future Cosmic Microwave Background
experiments aimed at observing its polarized emission. In particular, we focus
on the systematics induced by the beam and calibration, which are considered
the major sources of leakage from total intensity measurements to polarization.
We simulated synthetic data sets with Time-Ordered Astrophysics Scalable Tools,
a publicly available simulation and data analysis package. We also propose a
mitigation technique aiming at reducing the leakage by means of a template
fitting approach. This technique has shown promising results reducing the
leakage by 2 orders of magnitude at the power spectrum level when applied to a
realistic simulated data set of the LiteBIRD satellite mission. |
Slow-roll Inflation with the Gauss-Bonnet and Chern-Simons Corrections: We study slow-roll inflation with the Gauss-Bonnet and Chern-Simons
corrections. We obtain general formulas for the observables: spectral indices,
tensor-to-scalar ratio and circular polarization of gravitational waves. The
Gauss-Bonnet term violates the consistency relation r = -8n_T. Particularly,
blue spectrum n_T > 0 and scale invariant spectrum |8n_T|/r << 1 of tensor
modes are possible. These cases require the Gauss-Bonnet coupling function of
\xi _{,\phi } \sim 10^8/M_{Pl}. We use examples to show new-inflation-type
potential with 10M_{Pl} symmetry breaking scale and potential with flat region
in \phi \gtrsim 10M_{Pl} lead to observationally consistent blue and scale
invariant spectra, respectively. Hence, these interesting cases can actually be
realized. The Chern-Simons term produce circularly polarized tensor modes. We
show an observation of these signals supports existence of the Chern-Simons
coupling function of \omega _{,\phi } \sim 10^8/M_{Pl}. Thus, with future
observations, we can fix or constrain the value of these coupling functions, at
the CMB scale. | On Model Selection in Cosmology: We review some of the common methods for model selection: the goodness of
fit, the likelihood ratio test, Bayesian model selection using Bayes factors,
and the classical as well as the Bayesian information theoretic approaches. We
illustrate these different approaches by comparing models for the expansion
history of the Universe. In the discussion we highlight the premises and
objectives entering these different approaches to model selection and finally
recommend the information theoretic approach. |
Further understanding the interaction between dark energy and dark
matter: current status and future directions: The interaction between dark matter and dark energy can be incorporated into
field theory models of dark energy that have proved successful in alleviating
the coincidence problem. We review recent advances in this field, including new
models and constraints from different astronomical data sets. We show that
interactions are allowed by observations and can reduce the current tensions
among different measurements of cosmological parameters. We extend our
discussion to include constraints from non-linear effects and results from
cosmological simulations. Finally, we discuss forthcoming multi-messenger data
from current and future observational facilities that will help to improve our
understanding of the interactions within the dark sector. | New Constraints On Cosmic Polarization Rotation Including SPTpol B-mode
Polarization Observations: We present an update of the cosmic polarization rotation (CPR) constraint
from the recent SPTpol measurements of sub-degree B-mode polarization in the
cosmic microwave background (CMB) of 100 square degrees of sky. Our previous
CPR fluctuation constraint from the joint ACTpol-BICEP2-POLARBEAR polarization
data is 23.7 mrad (1.36{\deg}). With new SPTpol data included, the CPR
fluctuation constraint is updated to 17 mrad (1{\deg}) with the scalar to
tensor ratio r = - 0.05 +- 0.1 |
Pahs, Ionized Gas, and Molecular Hydrogen in Brightest Cluster Galaxies
of Cool Core Clusters of Galaxies: We present measurements of 5-25 {\mu}m emission features of brightest cluster
galaxies (BCGs) with strong optical emission lines in a sample of 9 cool-core
clusters of galaxies observed with the Infrared Spectrograph on board the
Spitzer Space Telescope. These systems provide a view of dusty molecular gas
and star formation, surrounded by dense, X-ray emitting intracluster gas. Past
work has shown that BCGs in cool-core clusters may host powerful radio sources,
luminous optical emission line systems, and excess UV, while BCGs in other
clusters never show this activity. In this sample, we detect polycyclic
aromatic hydrocarbons (PAHs), extremely luminous, rotationally-excited
molecular hydrogen line emission, forbidden line emission from ionized gas ([Ne
II] and [Ne III]), and infrared continuum emission from warm dust and cool
stars. We show here that these BCGs exhibit more luminous forbidden neon and H2
rotational line emission than star-forming galaxies with similar total infrared
luminosities, as well as somewhat higher ratios of 70 {\mu}m / 24 {\mu}m
luminosities. Our analysis suggests that while star formation processes
dominate the heating of the dust and PAHs, a heating process consistent with
suprathermal electron heating from the hot gas, distinct from star formation,
is heating the molecular gas and contributing to the heating of the ionized gas
in the galaxies. The survival of PAHs and dust suggests that dusty gas is
somehow shielded from significant interaction with the X-ray gas. | A New Equation of State for Dark Energy Model: A new parameterization for the dark energy equation of state(EoS) is proposed
and some of its cosmological consequences are also investigated. This new
parameterization is the modification of Efstathiou' dark energy EoS
parameterization. $w (z)$ is a well behaved function for $z\gg1$ and has same
behavior in $z$ at low redshifts with Efstathiou' parameterization. In this
parameterization there are two free parameter $w_0$ and $w_a$. We discuss the
constraints on this model's parameters from current observational data. The
best fit values of the cosmological parameters with $1\sigma$ confidence-level
regions are: $\Omega_m=0.2735^{+0.0171}_{-0.0163}$,
$w_0=-1.0537^{+0.1432}_{-0.1511}$ and $w_a=0.2738^{+0.8018}_{-0.8288}$. |
Canonical single field slow-roll inflation with a non-monotonic
tensor-to-scalar ratio: We take a pragmatic, model independent approach to single field slow-roll
canonical inflation by imposing conditions, not on the potential, but on the
slow-roll parameter $\epsilon(\phi)$ and its derivatives $\epsilon^{\prime
}(\phi)$ and $\epsilon^{\prime\prime }(\phi)$, thereby extracting general
conditions on the tensor-to-scalar ratio $r$ and the running $n_{sk}$ at
$\phi_{H}$ where the perturbations are produced, some $50$ $-$ $60$ $e$-folds
before the end of inflation. We find quite generally that for models where
$\epsilon(\phi)$ develops a maximum, a relatively large $r$ is most likely
accompanied by a positive running while a negligible tensor-to-scalar ratio
implies negative running. The definitive answer, however, is given in terms of
the slow-roll parameter $\xi_2(\phi)$. To accommodate a large tensor-to-scalar
ratio that meets the limiting values allowed by the Planck data, we study a
non-monotonic $\epsilon(\phi)$ decreasing during most part of inflation. Since
at $\phi_{H}$ the slow-roll parameter $\epsilon(\phi)$ is increasing, we thus
require that $\epsilon(\phi)$ develops a maximum for $\phi > \phi_{H}$ after
which $\epsilon(\phi)$ decrease to small values where most $e$-folds are
produced. The end of inflation might occur trough a hybrid mechanism and a
small field excursion $\Delta\phi_e\equiv |\phi_H-\phi_e |$ is obtained with a
sufficiently thin profile for $\epsilon(\phi)$ which, however, should not
conflict with the second slow-roll parameter $\eta(\phi)$. As a consequence of
this analysis we find bounds for $\Delta \phi_e$, $r_H$ and for the scalar
spectral index $n_{sH}$. Finally we provide examples where these considerations
are explicitly realised. | Hill-climbing dark inflation: Within the framework of the scalar-tensor theory we consider a hill-climbing
inflation, in which the effective Planck mass increases in time. We obtain the
Einstein frame potential with infinitely long and flat plateau as we approach
towards the strong coupling regime, together with a run-away vacuum in the GR
limit of the theory. The inflation ends with the scalar field rolling down
towards infinity, which at the effective level indicates the massless scalar
field domination in the Universe. In this scheme we assume that the inflaton is
a dark particle, which has no couplings to the Standard Model degrees of
freedom (other than the gravitational ones). We discuss the gravitational
reheating of the Universe together with its implications on the predictions of
the model, including possible amplification of primordial gravitational waves.
Our model for the first time realizes explicitly the enhancement of the
primordial gravitational waves in the dark inflation scenario. |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.