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Evolution of the pc-scale structure of PKS 1934-638 revisited: first
science with the ASKAP and New Zealand telescopes: We have studied the archetypal Gigahertz Peaked Spectrum radio galaxy, PKS
1934-638, using the Australian Long Baseline Array, augmented with two new
telescopes that greatly improve the angular resolution of the array. These VLBI
observations represent the first scientific results from a new antenna in NZ
and the first antenna of the Australian SKA Pathfinder (ASKAP). A compact
double radio source, PKS 1934-638, has been monitored over a period of 40
years, and the observation described here provides the latest datum, eight
years after the previous observation, to aid in the study of the long-term
evolution of the source structure. We take advantage of these new long
baselines to probe PKS 1934-638 at the relatively low frequency of 1.4 GHz, in
order to examine the effects of optical depth on the structure of the radio
source. Optical depth effects, resulting in the observation of frequency
dependent structure, may have previously been interpreted in terms of an
expansion of the source as a function of time. Expansion and frequency
dependent effects are important to disentangle in order to estimate the age of
PKS 1934-638. We show that frequency dependent structure effects are likely to
be important in PKS 1934-638 and present a simple two-dimensional synchrotron
source model in which opacity effects due to synchrotron self-absorption are
taken into account. Evidence for expansion of the radio source over 40 years is
therefore weak, with consequences for the estimated age of the radio source. | The clustering and evolution of H-alpha emitters at z~1 from HiZELS: (Abridged) The clustering properties of a well-defined sample of 734 H-alpha
emitters at z=0.84 obtained as part of the Hi-z Emission Line Survey (HiZELS)
are investigated. The spatial correlation function is very well-described by
(r/r_0)^-1.8, with r_0=2.7+-0.3Mpc/h. The correlation length r_0 increases
strongly with H-alpha luminosity, L_H-alpha, from r_0~2Mpc/h for the most
quiescent galaxies (star-formation rates of ~4M_sun/yr), up to r_0>5Mpc/h for
the brightest galaxies in H-alpha. The correlation length also increases with
increasing rest-frame K-band luminosity (M_K), but the r_0-L_H-alpha
correlation maintains its full statistical significance at fixed M_K. At
z=0.84, star-forming galaxies classified as irregulars or mergers are much more
clustered than discs and non-mergers, but once the samples are matched in
L_H-alpha and M_K, the differences vanish, implying that the clustering is
independent of morphological type at z~1. The typical H-alpha emitters found at
z=0.84 reside in dark-matter haloes of ~10^12M_sun, but those with the highest
SFRs reside in more massive haloes of ~10^13M_sun. Comparing the results with
those of H-alpha surveys at different redshifts, it is seen that although the
break of the H-alpha luminosity function, L*, evolves by a factor of ~30 from
z=0.24 to z=2.23, galaxies with the same L_H-alpha/L*(z) are found in dark
matter haloes of similar masses, independently of cosmic time. This not only
confirms that star-formation is more efficient at higher redshift, but also
suggests a fundamental connection between the strong decrease of L* since
z=2.23 and the quenching of star-formation in galaxies residing within
dark-matter haloes significantly more massive than 10^12M_sun at any given
epoch. |
Direct Estimate of the Post-Newtonian Parameter and Cosmic Curvature
from Galaxy-scale Strong Gravitational Lensing: Einstein's theory of general relativity (GR) has been precisely tested on
solar system scales, but extragalactic tests are still poorly performed. In
this work, we use a newly compiled sample of galaxy-scale strong gravitational
lenses to test the validity of GR on kiloparsec scales. In order to solve the
circularity problem caused by the preassumption of a specific cosmological
model based on GR, we employ the distance sum rule in the
Friedmann-Lema\^{\i}tre-Robertson-Walker metric to directly estimate the
parameterized post-Newtonian (PPN) parameter $\gamma_{\rm PPN}$ and the cosmic
curvature $\Omega_k$ by combining observations of strong lensing and Type Ia
supernovae. This is the first simultaneous measurement of $\gamma_{\rm PPN}$
and $\Omega_k$ without any assumptions about the contents of the universe or
the theory of gravity. Our results show that $\gamma_{\rm
PPN}=1.11^{+0.11}_{-0.09}$ and $\Omega_{k}=0.48^{+1.09}_{-0.71}$, indicating a
strong degeneracy between the two quantities. The measured $\gamma_{\rm PPN}$,
which is consistent with the prediction of 1 from GR, provides a precise
extragalactic test of GR with a fractional accuracy better than 9.0\%. If a
prior of the spatial flatness (i.e., $\Omega_{k}=0$) is adopted, the PPN
parameter constraint can be further improved to $\gamma_{\rm
PPN}=1.07^{+0.07}_{-0.07}$, representing a precision of 6.5\%. On the other
hand, in the framework of GR (i.e., $\gamma_{\rm PPN}=1$), our results are
still marginally compatible with zero curvature
($\Omega_k=-0.12^{+0.48}_{-0.36}$), supporting no significant deviation from a
flat universe. | Hubble Space Telescope spectra of the type Ia supernova SN2011fe: a tail
of low-density, high-velocity material with Z<Zsolar: Hubble Space Telescope spectroscopic observations of the nearby type Ia
supernova (SN Ia) SN2011fe, taken on 10 epochs from -13.1 to +40.8 days
relative to B-band maximum light, and spanning the far-ultraviolet (UV) to the
near-infrared (IR) are presented. This spectroscopic coverage makes SN2011fe
the best-studied local SN Ia to date. SN2011fe is a typical moderately-luminous
SN Ia with no evidence for dust extinction. Its near-UV spectral properties are
representative of a larger sample of local events (Maguire et al. 2012). The
near-UV to optical spectra of SN2011fe are modelled with a Monte Carlo
radiative transfer code using the technique of 'abundance tomography',
constraining the density structure and the abundance stratification in the SN
ejecta. SN2011fe was a relatively weak explosion, with moderate Fe-group
yields. The density structures of the classical model W7 and of a delayed
detonation model were tested. Both have shortcomings. An ad-hoc density
distribution was developed which yields improved fits and is characterised by a
high-velocity tail, which is absent in W7. However, this tail contains less
mass than delayed detonation models. This improved model has a lower energy
than one-dimensional explosion models matching typical SNe Ia (e.g. W7, WDD1).
The derived Fe abundance in the outermost layer is consistent with the
metallicity at the SN explosion site in M101 (~0.5 Zsolar). The spectroscopic
rise time (~19 days) is significantly longer than that measured from the early
optical light curve, implying a 'dark phase' of ~1 day. A longer rise time has
significant implications when deducing the properties of the white dwarf and
binary system from the early photometric behaviour. |
Precision modelling of the matter power spectrum in a Planck-like
Universe: We use a suite of high-resolution $N$-body simulations and state-of-the-art
perturbation theory to improve the code halofit, which predicts the nonlinear
matter power spectrum. We restrict attention to parameters in the vicinity of
the Planck Collaboration's best fit. On large-scales ($k\lesssim 0.07 h/{\rm
Mpc}$), our model evaluates the 2-loop calculation from the Multi-point
Propagator Theory of Bernardeau et al.(2012). On smaller scales ($k \gtrsim 0.7
h/{\rm Mpc}$), we transition to a smoothing-spline-fit model, that
characterises the differences between the Takahashi et al. (2012) recalibration
of halofit2012 and our simulations. We use an additional suite of simulations
to explore the response of the power spectrum to variations in the cosmological
parameters. In particular, we examine: the time evolution of the dark energy
equation of state ($w_0$, $w_a$); the matter density $\Omega_m$; the physical
densities of CDM and baryons $(\omega_c,\omega_b)$; and the primordial power
spectrum amplitude $A_s$, spectral index $n_s$, and its running $\alpha$. We
construct correction functions, which improve halofit's dependence on
cosmological parameters. Our newly calibrated model reproduces all of our data
with $\lesssim1\%$ precision. Including various systematic errors, such as
choice of $N$-body code, resolution, and through inspection of the scaled
second order derivatives, we estimate the accuracy to be $\lesssim3\%$ over the
hyper-cube: $w_0\in\{-1.05,-0.95\}$, $w_a\in\{-0.4,0.4\}$, $\Omega_{\rm
m,0}\in\{0.21,0.4\}$, $\omega_{\rm c}\in\{0.1,0.13\}$, $\omega_{\rm
b}\in\{2.0,2.4\}$, $n_{\rm s}\in\{0.85,1.05\}$, $A_s\in\{1.72\times
10^{-9},2.58\times 10^{-9}\}$, $\alpha\in\{-0.2,0.2\}$ up to $k=9.0 h/{\rm
Mpc}$ and out to $z=3$. Outside of this range the model reverts to halofit2012. | Did massive black holes in globular clusters initially satisfy galactic
scaling relations?: The masses of supermassive black holes (SMBHs, M_BH=10^6-10^11 Msun) in the
centres of galaxies are related to the host stellar spheroid mass and velocity
dispersion. A key question is how these relations originate, and over which
range of black hole masses they hold. It has been speculated that
intermediate-mass black holes (IMBHs, M_BH=10^2-10^5 Msun) could play a
fundamental role in the growth of SMBHs. A handful of IMBHs has recently been
detected in Galactic globular clusters (GCs), but their masses are inconsistent
with the galactic scaling relations of SMBHs. In this Letter, we derive the
initial properties of the GCs using a standard analytical evolutionary model,
of which the free parameters are fixed by independent constraints. We find that
the observed IMBH masses initially followed the galactic SMBH scaling
relations, and subsequently moved off these relations due to the dynamical
evolution of their host GCs. This work is concluded with a brief discussion of
the uncertainties and the implications of our results for the possible
universality of massive black hole growth. |
Non-linear Structure Formation for Dark Energy Models with a Steep
Equation of State: We study the nonlinear regime of large scale structure formation considering
a dynamical dark energy (DE) component determined by a Steep Equation of State
parametrization (SEoS) $w(z)=w_0+w_i\frac{(z/z_T)^q}{1+(z/z_T)^q}$. In order to
perform the model exploration at low computational cost, we modified the public
code L-PICOLA. We incorporate the DE model by means of the first and
second-order matter perturbations in the Lagrangian frame and the expansion
parameter. We analyze deviations of SEoS models with respect to $\Lambda$CDM in
the non-linear matter power spectrum ($P_k$), the halo mass function (HMF), and
the two-point correlation function (2PCF). On quantifying the nature of steep
(SEoS-I) and smooth transitions in DE field (CPL-lim), no signature of steep
transition is observed, rather found the overall impact of DE behaviors in
$P_k$ at level of $\sim 2-3\%$ and $\sim 3-4\%$ differences w.r.t $\Lambda$CDM
at $z=0$ respectively. HMF shows the possibility to distinguish between the
models at the high mass ends. The best-fitted model assuming only background
and linear perturbations dubbed as SEoS-II largely deviates from $\Lambda$CDM
and current observations on studying the nonlinear growth. This large deviation
in SEoS-II also quantified the combined effect of the dynamical DE and the
larger amount of matter contained, $\Omega_{m0}$ and $H_{0}$ accordingly. 2PCF
results are relatively robust with $\sim 1-2 \%$ deviation for SEoS-I and
CPL-lim and a significant deviation for SEoS-II throughout $r$ from
$\Lambda$CDM. Finally, we conclude that the search for viable DE models (like
the SEoS) must include non-linear growth constraints. | Quantified HI Morphology III: Merger Visibility Times from HI in Galaxy
Simulations: Major mergers of disk galaxies are thought to be a substantial driver in
galaxy evolution. To trace the fraction and the rate galaxies are in mergers
over cosmic times, several observational techniques, including morphological
selection criteria, have been developed over the last decade. We apply this
morphological selection of mergers to 21 cm radio emission line (HI) column
density images of spiral galaxies in nearby surveys. In this paper, we
investigate how long a 1:1 merger is visible in HI from N-body simulations. We
evaluate the merger visibility times for selection criteria based on four
parameters: Concentration, Asymmetry, M20, and the Gini parameter of second
order moment of the flux distribution (GM). Of three selection criteria used in
the literature, one based on Concentration and M20 works well for the HI
perspective with a merger time scale of 0.4 Gyr. Of the three selection
criteria defined in our previous paper, the GM performs well and cleanly
selects mergers for 0.69 Gyr. The other two criteria (A-M20 and C-M20), select
isolated disks as well, but perform best for face-on, gas-rich disks (T(merger)
~ 1 Gyr). The different visibility scales can be combined with the selected
fractions of galaxies in any large HI survey to obtain merger rates in the
nearby Universe. All-sky surveys such as WALLABY with ASKAP and the Medium Deep
Survey with the APETIF instrument on Westerbork are set to revolutionize our
perspective on neutral hydrogen and will provide an accurate measure of the
merger fraction and rate of the present epoch. |
Network analysis of the COSMOS galaxy field: The galaxy data provided by COSMOS survey for 1 by 1 degree field of sky are
analysed by methods of complex networks. Three galaxy samples (slices) with
redshifts ranging within intervals 0.88-0.91, 0.91-0.94 and 0.94-0.97 are
studied as two-dimensional projections for the spatial distributions of
galaxies. We construct networks and calculate network measures for each sample,
in order to analyse the network similarity of different samples, distinguish
various topological environments, and find associations between galaxy
properties (colour index and stellar mass) and their topological environments.
Results indicate a high level of similarity between geometry and topology for
different galaxy samples and no clear evidence of evolutionary trends in
network measures. The distribution of local clustering coefficient C manifests
three modes which allow for discrimination between stand-alone singlets and
dumbbells (0 <= C <= 0.1), intermediately (0 < C < 0.9) and clique (0.9 <= C <=
1) like galaxies. Analysing astrophysical properties of galaxies (colour index
and stellar masses), we show that distributions are similar in all slices,
however weak evolutionary trends can also be seen across redshift slices. To
specify different topological environments we have extracted selections of
galaxies from each sample according to different modes of C distribution. We
have found statistically significant associations between evolutionary
parameters of galaxies and selections of C: the distribution of stellar mass
for galaxies with interim C differ from the corresponding distributions for
stand-alone and clique galaxies, and this difference holds for all redshift
slices. The colour index realises somewhat different behaviour. | Cosmology with shear ratios: a joint study of weak lensing and
spectroscopic redshift datasets: The ratio of the average tangential shear signal of different weak lensing
source populations around the same lens galaxies, also known as a shear ratio,
provides an important test of lensing systematics and a potential source of
cosmological information. In this paper we measure shear ratios of three
current weak lensing surveys -- KiDS, DES, and HSC -- using overlapping data
from the Baryon Oscillation Spectroscopic Survey. We apply a Bayesian method to
reduce bias in shear ratio measurement, and assess the degree to which shear
ratio information improves the determination of important astrophysical
parameters describing the source redshift distributions and intrinsic galaxy
alignments, as well as cosmological parameters, in comparison with cosmic shear
and full 3x2-pt correlations (cosmic shear, galaxy-galaxy lensing, and galaxy
clustering). We consider both Fisher matrix forecasts, as well as full
likelihood analyses of the data. We find that the addition of shear ratio
information to cosmic shear allows the mean redshifts of the source samples and
intrinsic alignment parameters to be determined significantly more accurately.
Although the additional constraining power enabled by the shear ratio is less
than that obtained by introducing an accurate prior in the mean source redshift
using photometric redshift calibration, the shear ratio allows for a useful
cross-check. The inclusion of shear ratio data consistently benefits the
determination of cosmological parameters such as S_8, for which we obtain
improvements up to 34%. However these improvements are less significant when
shear ratio is combined with the full 3x2-pt correlations. We conclude that
shear ratio tests will remain a useful source of cosmological information and
cross-checks for lensing systematics, whose application will be further
enhanced by upcoming datasets such as the Dark Energy Spectroscopic Instrument. |
Finding and characterising WHIM structures using the luminosity density
method: We have developed a new method to approach the missing baryons problem. We
assume that the missing baryons reside in a form of Warm Hot Intergalactic
Medium, i.e. the WHIM. Our method consists of (a) detecting the coherent large
scale structure in the spatial distribution of galaxies that traces the Cosmic
Web and that in hydrodynamical simulations is associated to the WHIM, (b) map
its luminosity into a galaxy luminosity density field, (c) use numerical
simulations to relate the luminosity density to the density of the WHIM, (d)
apply this relation to real data to trace the WHIM using the observed galaxy
luminosities in the Sloan Digital Sky Survey and 2dF redshift surveys. In our
application we find evidence for the WHIM along the line of sight to the
Sculptor Wall, at redshifts consistent with the recently reported X-ray
absorption line detections. Our indirect WHIM detection technique complements
the standard method based on the detection of characteristic X-ray absorption
lines, showing that the galaxy luminosity density is a reliable signpost for
the WHIM. For this reason, our method could be applied to current galaxy
surveys to optimise the observational strategies for detecting and studying the
WHIM and its properties. Our estimates of the WHIM hydrogen column density in
Sculptor agree with those obtained via the X-ray analysis. Due to the
additional column density estimate, our method has potential for improving the
constrains of the physical parameters of the WHIM as derived with X-ray
absorption, and thus for improving the understanding of the missing baryons
problem. | A case study for measuring the relativistic dipole of a galaxy
cross-correlation with the Dark Energy Spectroscopic Instrument: The data on spectroscopic galaxy clustering collected by the Dark Energy
Spectroscopic Instrument (DESI) will allow the significant detection of subtle
features in the galaxy two-point correlation in redshift space, beyond the
"standard" redshift-space distortions. Here we present an independent
assessment of the detectability of the relativistic dipole in the
cross-correlation of two populations of galaxies if they would be selected from
the Bright Galaxy Survey (BGS) of DESI. We build synthetic galaxy catalogues
with the characteristics of the BGS using the light cone of a relativistic
$N$-body simulation. Exploring different ways of splitting the populations of
galaxies we find that with an unequal split with more bright galaxies than
faint galaxies the detectability is significantly boosted, reaching 19 $\sigma$
in the redshift bin $0.2 \lesssim z \lesssim 0.3$ and expected to be even
higher at lower redshift. Moreover, we find that the measured dipole agrees
very well with the prediction of relativistic effects from linear theory down
to separations of $\sim$ 30 Mpc/$h$. |
Evolution of CMB spectral distortion anisotropies and tests of
primordial non-Gaussianity: Anisotropies in distortions to the frequency spectrum of the cosmic microwave
background (CMB) can be created through spatially varying heating processes in
the early Universe. For instance, the dissipation of small-scale acoustic modes
does create distortion anisotropies, in particular for non-Gaussian primordial
perturbations. In this work, we derive approximations that allow describing the
associated distortion field. We provide a systematic formulation of the problem
using Fourier-space window functions, clarifying and generalizing previous
approximations. Our expressions highlight the fact that the amplitudes of the
spectral-distortion fluctuations induced by non-Gaussianity depend also on the
homogeneous value of those distortions. Absolute measurements are thus required
to obtain model-independent distortion constraints on primordial
non-Gaussianity. We also include a simple description for the evolution of
distortions through photon diffusion, showing that these corrections can
usually be neglected. Our formulation provides a systematic framework for
computing higher order correlation functions of distortions with CMB
temperature anisotropies and can be extended to describe correlations with
polarization anisotropies. | The optimal weighting function for cosmic magnification measurement
through foreground galaxy-background galaxy (quasar) cross correlation: Cosmic magnification has been detected through cross correlation between
foreground and background populations (galaxies or quasars). It has been shown
that weighing each background object by its $\alpha-1$ can significantly
improve the cosmic magnification measurement \citep{Menard02,Scranton05}. Here,
$\alpha$ is the logarithmic slope of the luminosity function of background
populations. However, we find that this weighting function is optimal only for
sparse background populations in which intrinsic clustering is negligible with
respect to shot noise. We derive the optimal weighting function for general
case including scale independent and scale dependent weights. The optimal
weighting function improves the S/N (signal to noise ratio) by $\sim 20%$ for a
BigBOSS-like survey and the improvement can reach a factor of $\sim 2$ for
surveys with much denser background populations. |
Effect of primordial magnetic fields on the ionization history: Primordial magnetic fields (PMF) damp at scales smaller than the photon
diffusion and free-streaming scale. This leads to heating of ordinary matter
(electrons and baryons), which affects both the thermal and ionization history
of our Universe. Here, we study the effect of heating due to ambipolar
diffusion and decaying magnetic turbulence. We find that changes to the
ionization history computed with recfast are significantly overestimated when
compared with CosmoRec. The main physical reason for the difference is that the
photoionization coefficient has to be evaluated using the radiation temperature
rather than the matter temperature. A good agreement with CosmoRec is found
after changing this aspect. Using Planck 2013 data and considering only the
effect of PMF-induced heating, we find an upper limit on the r.m.s. magnetic
field amplitude of B0 < 1.1 nG (95% c.l.) for a stochastic background of PMF
with a nearly scale-invariant power spectrum. We also discuss uncertainties
related to the approximations for the heating rates and differences with
respect to previous studies. Our results are important for the derivation of
constraints on the PMF power spectrum obtained from measurements of the cosmic
microwave background anisotropies with full-mission Planck data. They may also
change some of the calculations of PMF-induced effects on the primordial
chemistry and 21cm signals. | The Cosmic Thermal History Probed by Sunyaev-Zeldovich Effect Tomography: The cosmic thermal history, quantified by the evolution of the mean thermal
energy density in the universe, is driven by the growth of structures as
baryons get shock heated in collapsing dark matter halos. This process can be
probed by redshift-dependent amplitudes of the thermal Sunyaev-Zeldovich (SZ)
effect background. To do so, we cross-correlate eight sky intensity maps in the
$\it{Planck}$ and Infrared Astronomical Satellite missions with two million
spectroscopic redshift references in the Sloan Digital Sky Surveys. This
delivers snapshot spectra for the far-infrared to microwave background light as
a function of redshift up to $z\sim3$. We decompose them into the SZ and
thermal dust components. Our SZ measurements directly constrain $\langle
bP_{\rm e} \rangle$, the halo bias-weighted mean electron pressure, up to
$z\sim 1$. This is the highest redshift achieved to date, with uncorrelated
redshift bins thanks to the spectroscopic references. We detect a threefold
increase in the density-weighted mean electron temperature $\bar{T}_{\rm{e}}$
from $7\times 10^5~{\rm K}$ at $z=1$ to $2\times 10^6~{\rm K}$ today. Over
$z=1$-$0$, we witness the build-up of nearly $70\%$ of the present-day mean
thermal energy density $\rho_{\rm{th}}$, with the corresponding density
parameter $\Omega_{\rm th}$ reaching $1.5 \times10^{-8}$. We find the mass bias
parameter of $\it{Planck}$'s universal pressure profile of $B=1.27$ (or
$1-b=1/B=0.79$), consistent with the magnitude of non-thermal pressure in gas
motion and turbulence from mass assembly. We estimate the redshift-integrated
mean Compton parameter $y\sim1.2\times10^{-6}$, which will be tested by future
spectral distortion experiments. More than half of which originates from the
large-scale structure at $z<1$, which we detect directly. |
The XMM Cluster Survey: Automating the estimation of hydrostatic mass
for large samples of galaxy clusters I -- Methodology, Validation, &
Application to the SDSSRM-XCS sample: We describe features of the X-ray: Generate and Analyse (XGA) open-source
software package that have been developed to facilitate automated hydrostatic
mass ($M_{\rm hydro}$) measurements from XMM X-ray observations of clusters of
galaxies. This includes describing how XGA measures global, and radial, X-ray
properties of galaxy clusters. We then demonstrate the reliability of XGA by
comparing simple X-ray properties, namely the X-ray temperature and gas mass,
with published values presented by the XMM Cluster Survey (XCS), the Ultimate
XMM eXtragaLactic survey project (XXL), and the Local Cluster Substructure
Survey (LoCuSS). XGA measured values for temperature are, on average, within 1%
of the values reported in the literature for each sample. XGA gas masses for
XXL clusters are shown to be ${\sim}$10% lower than previous measurements
(though the difference is only significant at the $\sim$1.8$\sigma$ level),
LoCuSS $R_{2500}$ and $R_{500}$ gas mass re-measurements are 3% and 7% lower
respectively (representing a 1.5$\sigma$ and 3.5$\sigma$ difference).
Like-for-like comparisons of hydrostatic mass are made to LoCuSS results, which
show that our measurements are $10{\pm}3%$ ($19{\pm}7%$) higher for $R_{2500}$
($R_{500}$). The comparison between $R_{500}$ masses shows significant scatter.
Finally, we present new $M_{\rm hydro}$ measurements for 104 clusters from the
SDSS DR8 redMaPPer XCS sample (SDSSRM-XCS). Our SDSSRM-XCS hydrostatic mass
measurements are in good agreement with multiple literature estimates, and
represent one of the largest samples of consistently measured hydrostatic
masses. We have demonstrated that XGA is a powerful tool for X-ray analysis of
clusters; it will render complex-to-measure X-ray properties accessible to
non-specialists. | Cosmology on Ultralarge Scales with Intensity Mapping of the Neutral
Hydrogen 21 cm Emission: Limits on Primordial Non-Gaussianity: The large-scale structure of the Universe supplies crucial information about
the physical processes at play at early times. Unresolved maps of the intensity
of 21 cm emission from neutral hydrogen HI at redshifts z~1-5 are the best hope
of accessing the ultralarge-scale information, directly related to the early
Universe. A purpose-built HI intensity experiment may be used to detect the
large scale effects of primordial non-Gaussianity, placing stringent bounds on
different models of inflation. We argue that it may be possible to place tight
constraints on the non-Gaussianity parameter f_NL, with an error close to ~1. |
Reconstructing quintom from WMAP 5-year observations: Generalized ghost
condensate: In the 5-year WMAP data analysis, a new parametrization form for dark energy
equation-of-state was used, and it has been shown that the equation-of-state,
$w(z)$, crosses the cosmological-constant boundary $w=-1$. Based on this
observation, in this paper, we investigate the reconstruction of quintom dark
energy model. As a single-real-scalar-field model of dark energy, the
generalized ghost condensate model provides us with a successful mechanism for
realizing the quintom-like behavior. Therefore, we reconstruct this
scalar-field quintom dark energy model from the WMAP 5-year observational
results. As a comparison, we also discuss the quintom reconstruction based on
other specific dark energy ansatzs, such as the CPL parametrization and the
holographic dark energy scenarios. | Jeans Analysis of Bok globules in $f(R)$ gravity: We examine the effects of $f(R)$ gravity on Jeans analysis of collapsing dust
clouds. We provide a method for testing modified gravity models by their
effects on star formation as the presence of $f(R)$ gravity is found to modify
the limit for collapse. In this analysis we add perturbations to a de Sitter
background. Depending on the characteristics of a chosen $f(R)$ model, the
appearance of new limits is possible. The physicality of these limits is
further examined. We find the asymptotic Jeans masses for $f(R)$ theories
compared to standard Jeans mass. Through this ratio, the effects of the $f(R)$
modified Jeans mass for viable theories are examined in molecular clouds. Bok
globules have a mass range comparable to Jeans masses in question and are
therefore used for comparing different $f(R)$ models. Viable theories are found
to assist in star formation. |
The Properties of the Heterogeneous Shakhbazyan Groups of Galaxies in
the SDSS: We present a systematic study of the sub-sample of Shakhbazyan groups (SHKs)
covered by the Sloan Digital Sky Survey Data Release--5 (SDSS-5). SHKs probe an
environment with characteristics which are intermediate between those of loose
and very compact groups. Surprisingly, we found that several groups identifying
algorithms (e.g. Berlind et al. 2006, Tago et al. 2008) miss this type of
structures. Using the SDSS-5 spectroscopic data and the photometric redshifts
derived in D'Abrusco et al. 2007, we identified possible group members in
photometric redshift space and derived, for each group, several individual
properties. We also combined pointed and stacked Rosat All Sky Survey data to
investigate the X-ray luminosities of these systems. Our study confirms that
the majority of groups are physical entities with richness in the range 3--13
galaxies, and properties ranging between those of loose and compact groups. We
confirm that SHK groups are richer in early-type galaxies than the surrounding
environment and the field, as expected from the morphology-density relation and
from the selection of groups of red galaxies. Furthermore, our work supports
the existence of two sub-classes of structures, the first one being formed by
compact and isolated groups and the second formed by extended structures. We
suggest that while the first class of objects dwells in less dense regions like
the outer parts of clusters or the field, possibly sharing the properties of
Hickson Compact Groups, the more extended structures represent a mixture of
[core+halo] configurations and cores of rich clusters. X-ray luminosities for
SHKs are generally consistent with these results and with the expectations for
the L_X-sigma_v relation, but also suggest the velocity dispersions reported in
literature are underestimated for some of the richest systems. | Mass-dependent evolution of the relation between supermassive black hole
mass and host spheroid mass since z ~ 1: We investigate the evolution of supermassive black hole mass (M_BH) and the
host spheroid mass (M_sph) in order to track the history of the M_BH-M_sph
relationship. The typical mass increase of M_BH is calculated by a continuity
equation and accretion history, which is estimated from the active galactic
nucleus (AGN) luminosity function. The increase in M_sph is also calculated by
using a continuity equation and a star formation model, which uses
observational data for the formation rate and stellar mass function. We find
that the black hole to spheroid mass ratio is expected to be substantially
unchanged since z~1.2 for high mass objects (M_BH>10^8.5M_SUN and
M_sph>10^11.3M_SUN). In the same redshift range, the spheroid mass is found to
increase more rapidly than the black hole mass if M_sph>10^11M_SUN. The
proposed mass-dependent model is consistent with the current available
observational data in the M_BH-M_sph diagram. |
Rapid Simulations of Halo and Subhalo Clustering: The analysis of cosmological galaxy surveys requires realistic simulations
for their interpretation. Forward modelling is a powerful method to simulate
galaxy clustering without the need for an underlying complex model. This
approach requires fast cosmological simulations with a high resolution and
large volume, to resolve small dark matter halos associated to single galaxies.
In this work, we present fast halo and subhalo clustering simulations based on
the Lagrangian perturbation theory code PINOCCHIO, which generates halos and
merger trees. The subhalo progenitors are extracted from the merger history and
the survival of subhalos is modelled. We introduce a new fitting function for
the subhalo merger time, which includes a redshift dependence of the fitting
parameters. The spatial distribution of subhalos within their hosts is modelled
using a number density profile. We compare our simulations with the halo finder
ROCKSTAR applied to the full N-body code GADGET-2. The subhalo velocity
function and the correlation function of halos and subhalos are in good
agreement. We investigate the effect of the chosen number density profile on
the resulting subhalo clustering. Our simulation is approximate yet realistic
and significantly faster compared to a full N-body simulation combined with a
halo finder. The fast halo and subhalo clustering simulations offer good
prospects for galaxy forward models using subhalo abundance matching. | The Kinetic Sunyaev-Zel'dovich effect as a probe of the physics of
cosmic reionization: the effect of self-regulated reionization: We calculate the angular power spectrum of the Cosmic Microwave Background
(CMB) temperature fluctuations induced by the kinetic Sunyaev-Zel'dovich (kSZ)
effect from the epoch of reionization (EOR). We use detailed N-body+radiative
transfer simulations to follow inhomogeneous reionization of the intergalactic
medium (IGM). For the first time we take into account the "self-regulation" of
reionization: star formation in low-mass dwarf galaxies (10^8 M_\sun \lesssim M
\lesssim 10^9 M_\sun) or minihalos (10^5 M_\sun \lesssim M \lesssim 10^8
M_\sun) is suppressed if these halos form in the regions that were already
ionized or Lyman-Werner dissociated. Some previous work suggested that the
amplitude of the kSZ power spectrum from the EOR can be described by a
two-parameter family: the epoch of half ionization and the duration of
reionization. However, we argue that this picture applies only to simple forms
of the reionization history which are roughly symmetric about the
half-ionization epoch. In self-regulated reionization, the universe begins to
be ionized early, maintains a low level of ionization for an extended period,
and then finishes reionization as soon as high-mass atomically-cooling halos
dominate. While inclusion of self-regulation affects the amplitude of the kSZ
power spectrum only modestly (\sim 10 %), it can change the duration of
reionization by a factor of more than two. We conclude that the simple
two-parameter family does not capture the effect of a physical, yet complex,
reionization history caused by self-regulation. When added to the
post-reionization kSZ contribution, our prediction for the total kSZ power
spectrum is below the current upper bound from the South Pole Telescope.
Therefore, the current upper bound on the kSZ effect from the EOR is consistent
with our understanding of the physics of reionization. |
The nuclear physics of OHe: A recent composite-dark-matter scenario assumes that the dominant fraction of
dark matter consists of O-helium (OHe) dark atoms, in which a lepton-like
doubly charged particle O is bound with a primordial helium nucleus. It
liberates the physics of dark matter from unknown features of new physics, but
it demands a deep understanding of the details of known nuclear and atomic
physics, which are still unclear. Here, we consider in detail the physics of
the binding of OHe to various nuclei of interest for direct dark matter
searches. We show that standard quantum mechanics leads to bound states in the
keV region, but does not seem to provide a simple mechanism that stabilizes
them. The crucial role of a barrier in the OHe-nucleus potential is confirmed
for such a stabilization. | Unearthing Foundations of a Cosmic Cathedral: Searching the Stars for
M33's Halo: We use data from the Pan-Andromeda Archaeological Survey (PAndAS) to search
for evidence of an extended halo component belonging to M33 (the Triangulum
Galaxy). We identify a population of red giant branch (RGB) stars at large
radii from M33's disk whose connection to the recently discovered extended
"disk substructure" is ambiguous, and which may represent a "bona-fide" halo
component. After first correcting for contamination from the Milky Way
foreground population and misidentified background galaxies, we average the
radial density of RGB candidate stars over circular annuli centered on the
galaxy and away from the disk substructure. We find evidence of a
low-luminosity, centrally concentrated component that is everywhere in our data
fainter than mu_V ~ 33 mag arcsec^(-2). The scale length of this feature is not
well constrained by our data, but it appears to be of order r_exp ~ 20 kpc;
there is weak evidence to suggest it is not azimuthally symmetric. Inspection
of the overall CMD for this region that specifically clips out the disk
substructure reveals that this residual RGB population is consistent with an
old population with a photometric metallicity of around [Fe/H] ~ -2 dex, but
some residual contamination from the disk substructure appears to remain. We
discuss the likelihood that our findings represent a bona-fide halo in M33,
rather than extended emission from the disk substructure. We interpret our
findings in terms of an upper limit to M33's halo that is a few percent of its
total luminosity, although its actual luminosity is likely much less. |
Extracting the Global 21-cm signal from Cosmic Dawn and Epoch of
Reionization in the presence of Foreground and Ionosphere: Detection of redshifted \ion{H}{i} 21-cm emission is a potential probe for
investigating the Universe's first billion years. However, given the
significantly brighter foreground, detecting 21-cm is observationally
difficult. The Earth's ionosphere considerably distorts the signal at low
frequencies by introducing directional-dependent effects. Here, for the first
time, we report the use of Artificial Neural Networks (ANNs) to extract the
global 21cm signal characteristics from the composite all-sky averaged signal,
including foreground and ionospheric effects such as refraction, absorption,
and thermal emission from the ionosphere's F and D-layers. We assume a
'perfect' instrument and neglect instrumental calibration and beam effects. To
model the ionospheric effect, we considered the static and time-varying
ionospheric conditions for the mid-latitude region where LOFAR is situated. In
this work, we trained the ANN model for various situations using a synthetic
set of the global 21cm signals created by altering its parameter space based on
the "$\rm \tanh$" parameterized model and the Accelerated Reionization Era
Simulations (ARES) algorithm. The obtained result shows that the ANN model can
extract the global signal parameters with an accuracy of $\ge 96 \% $ in the
final study when we include foreground and ionospheric effects. On the other
hand, a similar ANN model can extract the signal parameters from the final
prediction dataset with an accuracy ranging from $97 \%$ to $98 \%$ when
considering more realistic sets of the global 21cm signals based on physical
models. | Cyclic cosmology from Lagrange-multiplier modified gravity: We investigate cyclic and singularity-free evolutions in a universe governed
by Lagrange-multiplier modified gravity, either in scalar-field cosmology, as
well as in $f(R)$ one. In the scalar case, cyclicity can be induced by a
suitably reconstructed simple potential, and the matter content of the universe
can be successfully incorporated. In the case of $f(R)$-gravity, cyclicity can
be induced by a suitable reconstructed second function $f_2(R)$ of a very
simple form, however the matter evolution cannot be analytically handled.
Furthermore, we study the evolution of cosmological perturbations for the two
scenarios. For the scalar case the system possesses no wavelike modes due to a
dust-like sound speed, while for the $f(R)$ case there exist an oscillation
mode of perturbations which indicates a dynamical degree of freedom. Both
scenarios allow for stable parameter spaces of cosmological perturbations
through the bouncing point. |
Local analyses of Planck maps with Minkowski Functionals: Minkowski Functionals (MF) are excellent tools to investigate the statistical
properties of the cosmic background radiation (CMB) maps. Between their
notorious advantages is the possibility to use them efficiently in patches of
the CMB sphere, which allow studies in masked skies, inclusive analyses of
small sky regions. Then, possible deviations from Gaussianity are investigated
by comparison with MF obtained from a set of Gaussian isotropic simulated CMB
maps to which are applied the same cut-sky masks. These analyses are sensitive
enough to detect contaminations of small intensity like primary and secondary
CMB anisotropies. Our methodology uses the MF, widely employed to study
non-Gaussianities in CMB data, and asserts Gaussian deviations only when all of
them points out an exceptional $\chi^2$ value, at more than $2.2 \sigma$
confidence level, in a given sky patch. Following this rigorous procedure, we
find 13 regions in the foreground-cleaned Planck maps that evince such high
levels of non-Gaussian deviations. According to our results, these non-Gaussian
contributions show signatures that can be associated to the presence of hot or
cold spots in such regions. Moreover, some of these non-Gaussian deviations
signals suggest the presence of foreground residuals in those regions located
near the galactic plane. Additionally, we confirm that most of the regions
revealed in our analyses, but not all, have been recently reported in studies
done by the Planck collaboration. Furthermore, we also investigate whether
these non-Gaussian deviations can be possibly sourced by systematics, like
inhomogeneous noise and beam effect in the released Planck data, or perhaps due
to residual galactic foregrounds. | Phenomenology of the Invisible Universe: Cosmology is operating now on a well established and tightly constraining
empirical basis. The relativistic LambdaCDM hot big bang theory is consistent
with all the present tests; it has become the benchmark. But the many open
issues in this subject make it reasonable to expect that a more accurate
cosmology will have more interesting physics in the invisible sector of the
universe, and maybe also in the visible part. |
Limit on the dark matter mass from its interaction with photons: In this work, we explore the phenomenology of generalized dark matter (GDM)
which interacts with photons ($\gamma$). We assume that DM establishes elastic
scattering with $\gamma$ when it has already become nonrelativistic, otherwise
the abundance of DM today is disfavored by current observations. Within this
scenario, the equation of state (EoS) of DM is determined by its mass
($m_\chi$) and the DM-$\gamma$ scattering cross-section. The distinctive
imprints of a nonzero EoS of DM on CMB angular power spectrum allow us to set a
lower limit on $m_\chi$ with Planck 2018 data alone, i.e., $m_{\chi} > 8.7$ keV
at $95\%$ C.L. In the study of cosmic concordance problems, we find that the
GDM scenario preserves the sound horizon ($r_s(z_*)$) predicted in the fiducial
$\Lambda$CDM model, and thus does not solve the $H_0$ tension. When performing
the joint analysis of Planck+LSS datasets, the best-fit $S_8= 0.785\pm 0.017$
closely matches the given $S_8$ prior. This suggests that the GDM scenario can
be counted as a viable candidate to restore the $S_8$ ($\sigma_{8}$) tension. | Cosmological impact of microwave background temperature measurements: The cosmic microwave background temperature is a cornerstone astrophysical
observable. Its present value is tightly constrained, but its redshift
dependence, which can now be determined until redshift $z\sim6.34$, is also an
important probe of fundamental cosmology. We show that its constraining power
is now comparable to that of other background cosmology probes, including Type
Ia supernovae and Hubble parameter measurements. We illustrate this with three
models, each based on a different conceptual paradigm, which aim to explain the
recent acceleration of the universe. We find that for parametric extension of
$\Lambda$CDM the combination of temperature and cosmological data significantly
improves constraints on the model parameters, while for alternative models
without a $\Lambda$CDM limit this data combination rules them out. |
The DESI One-Percent Survey: Exploring the Halo Occupation Distribution
of Luminous Red Galaxies and Quasi-Stellar Objects with AbacusSummit: We present the first comprehensive Halo Occupation Distribution (HOD)
analysis of the DESI One-Percent survey Luminous Red Galaxy (LRG) and
Quasi-Stellar Object (QSO) samples. We constrain the HOD of each sample and
test possible HOD extensions by fitting the redshift-space galaxy 2-point
correlation functions in 0.15 < r < 32 Mpc/h in a set of fiducial redshift
bins. We use AbacusSummit cubic boxes at Planck 2018 cosmology as model
templates and forward model galaxy clustering with the AbacusHOD package. We
achieve good fits with a standard HOD model with velocity bias, and we find no
evidence for galaxy assembly bias or satellite profile modulation at the
current level of statistical uncertainty. For LRGs in 0.4 < z < 0.6, we infer a
satellite fraction of fsat = 11+-1%, a mean halo mass of log10 Mh =
13.40+0.02-0.02, and a linear bias of blin = 1.93+0.06-0.04. For LRGs in 0.6 <
z < 0.8, we find fsat = 14+-1%, log10 Mh = 13.24+0.02-0.02, and blin =
2.08+0.03-0.03. For QSOs, we infer fsat = 3+8-2%, log10 Mh = 12.65+0.09-0.04,
and blin = 2.63+0.37-0.26 in redshift range 0.8 < z < 2.1. Using these fits, we
generate a large suite of high-fidelity galaxy mocks. We also study the
redshift-evolution of the DESI LRG sample from z = 0.4 up to z = 1.1, revealing
significant and interesting trends in mean halo mass, linear bias, and
satellite fraction. | An efficient probe of the cosmological CPT violation: We develop an efficient method based on the linear regression algorithm to
probe the cosmological CPT violation using the CMB polarisation data. We
validate this method using simulated CMB data and apply it to recent CMB
observations. We find that a combined data sample of BICEP1 and BOOMERanG 2003
favours a nonzero isotropic rotation angle at $2.3\sigma$ confidence level, ie,
$\Delta\alpha=-3.3 \pm1.4$ deg (68% CL) with systematics included. |
Cosmological constraints on Lorentz invariance violation in the neutrino
sector: We derive the Boltzmann equation in the synchronous gauge for massive
neutrinos with a deformed dispersion relation. Combining the 7-year WMAP data
with lower-redshift measurements of the expansion rate, we give constraints on
the deformation parameter and find that the deformation parameter is strong
degenerate with the physical dark matter density instead of the neutrino mass.
Our results show that there is no evidence for Lorentz invariant violation in
the neutrino sector. The ongoing Planck experiment could provide improved
constraints on the deformation parameter. | Intragroup dark matter distribution in small groups of halos in a LCDM
cosmology: We study the distribution of intragroup dark matter in small groups of dark
matter halos of galaxy-like size in a LCDM cosmology. These groups are
identified using a physical criterion and may be an appropriate representation
of small galaxy groups. We quantify the amount of intragroup dark matter and
characterize its distribution. We find that compact associations of halos, as
well as those intermediate and loose groups, have rather flat intragroup dark
matter profiles with logarithmic slopes of gamma ~0 and ~-0.2$, respectively.
Hence, the intragroup dark matter of these halo systems does not follow the
same cuspy tendency that halos of galaxies have. In intermediate and loose
galaxy-size halo associations the intragroup matter tends to be <50% that of
the total mass of the group, and in compact associations is <20% within their
group radius. |
The case for testing MOND using LISA Pathfinder: We quantify the potential for testing MOdified Newtonian Dynamics (MOND) with
LISA Pathfinder (LPF), should a saddle point flyby be incorporated into the
mission. We forecast the expected signal to noise ratio (SNR) for a variety of
instrument noise models and trajectories past the saddle. For standard
theoretical parameters the SNR reaches middle to high double figures even with
modest assumptions about instrument performance and saddle approach. Obvious
concerns, like systematics arising from LPF self-gravity, or the Newtonian
background, are examined and shown not to be a problem. We also investigate the
impact of a negative observational result upon the free-function determining
the theory. We demonstrate that, if Newton's gravitational constant is
constrained not be re-normalized by more than a few percent, only contrived
MONDian free-functions would survive a negative result. There are exceptions,
e.g. free-functions not asymptoting to 1 in the Newtonian limit, but rather
diverging or asymptoting to zero (depending on their mother relativistic
MONDian theory). Finally, we scan the structure of all proposed relativistic
MONDian theories, and classify them with regards to their non-relativistic
limit, finding three broad cases (with a few sub-cases depending on the form of
the free function). It is appears that only the Einstein-Aether formulation,
and the sub-cases where the free-function does not asymptote to 1 in other
theories, would survive a negative result without resorting to "designer"
free-functions. | The primordial black hole from running curvaton: In light of our previous work \cite{Liu:2019xhn}, we investigate the
possibility of the formation of a primordial black hole in the second
inflationary process induced by the oscillation of curvaton. By adopting the
instability of the Mathieu equation, one could utilize the $\delta$ function to
fully describe the power spectrum. Due to the running of curvaton mass, we can
simulate the value of abundance of primordial black holes nearly covering all
of the mass ranges, in which we have given three special cases. One case could
account for the dark matter in some sense since the abundance of a primordial
black hole is about $75\%$. At late times, the relic of exponential potential
could be approximated to a constant of the order of cosmological constant
dubbed as a role of dark energy. Thus, our model could unify dark energy and
dark matter from the perspective of phenomenology. Finally, it sheds new light
on exploring Higgs physics. |
Axion as a cold dark matter candidate: low-mass case: Axion as a coherently oscillating scalar field is known to behave as a cold
dark matter in all cosmologically relevant scales. For conventional axion mass
with 10^{-5} eV, the axion reveals a characteristic damping behavior in the
evolution of density perturbations on scales smaller than the solar system
size. The damping scale is inversely proportional to the square-root of the
axion mass. We show that the axion mass smaller than 10^{-24} eV induces a
significant damping in the baryonic density power spectrum in cosmologically
relevant scales, thus deviating from the cold dark matter in the scale smaller
than the axion Jeans scale. With such a small mass, however, our basic
assumption about the coherently oscillating scalar field is broken in the early
universe. This problem is shared by other dark matter models based on the
Bose-Einstein condensate and the ultra-light scalar field. We introduce a
simple model to avoid this problem by introducing evolving axion mass in the
early universe, and present observational effects of present-day low-mass axion
on the baryon density power spectrum, the cosmic microwave background radiation
(CMB) temperature power spectrum, and the growth rate of baryon density
perturbation. In our low-mass axion model we have a characteristic small-scale
cutoff in the baryon density power spectrum below the axion Jeans scale. The
small-scale deviations from the cold dark matter model in both matter and CMB
power spectra clearly differ from the ones expected in the cold dark matter
model mixed with the massive neutrinos as a hot dark matter component. | What could the value of the cosmological constant tell us about the
future variation of the fine structure constant?: Motivated by reported claims of the measurements of a variation of the fine
structure constant $\alpha$ we consider a theory where the electric charge, and
consequently $\alpha$, is not a constant but depends on the Ricci scalar $R$.
%We then show how this can be considered a particular case of the Bekenstein
theory in which there is no need to %introduce an additional kinetic term for
the scalar field associated to the electric charge, since the Einstein's%
%equations are sufficient to determine the geometry and, consequently the Ricci
scalar. We then study the cosmological implications of this theory, considering
in particular the effects of dark energy and of a cosmological constant on the
evolution of $\alpha$. Some low-red shift expressions for the variation of
$\alpha(z)$ are derived, showing the effects of the equation of state of dark
energy on $\alpha$ and observing how future measurements of the variation of
the fine structure constant could be used to determine indirectly the equation
of state of dark energy and test this theory. In the case of a $\Lambda CDM$
Universe, according to the current estimations of the cosmological parameters,
the present value of the Ricci scalar is $\approx 10%$ smaller than its future
asymptotic value determined by the value of the cosmological constant, setting
also a bound on the future asymptotic value of $\alpha$. |
A 2.5-5 μm Spectroscopic Study of Hard X-ray Selected AGNs using
AKARI InfraRed Camera: We present results of the 2.5-5 {\mu}m spectroscopy of a sample of hard X-ray
selected active galactic nuclei (AGNs) using the grism mode of the InfraRed
Camera (IRC) on board the infrared astronomical satellite AKARI. The sample is
selected from the 9-month Swift/BAT survey in the 14-195 keV band, which
provides a fair sample of AGNs including highly absorbed ones. The 2.5-5 {\mu}m
spectroscopy provide a strong diagnostic tool for the circumnuclear environment
of AGNs through the continuum shapes and emission/absorption features such as
the 3.3 {\mu}m polycyclic aromatic hydrocarbon (PAH) emission and the broad 3.1
{\mu}m H2O ice, 3.4 {\mu}m bare carbonaceous dust, 4.26 {\mu}m CO2 and 4.67
{\mu}m CO absorptions. As our first step, we use the 3.3 {\mu}m PAH emission as
a proxy for the star-formation activity and searched for possible difference of
star-formation activity between type 1 (unabsorbed) and type 2 (absorbed) AGNs.
We found no significant dependence of the 3.3 {\mu}m PAH line luminosity,
normalized by the black hole mass, on optical AGNs types or the X-ray measured
column densities. | Scaling relations of metallicity, stellar mass, and star formation rate
in metal-poor starbursts: II. Theoretical models: Scaling relations of metallicity (O/H), star formation rate (SFR), and
stellar mass give important insight on galaxy evolution. They are obeyed by
most galaxies in the Local Universe and also at high redshift. In a companion
paper, we compiled a sample of ~1100 galaxies from redshift 0 to ~3, spanning
almost two orders of magnitude in metal abundance, a factor of $\sim10^6$ in
SFR, and of ~10^5 in stellar mass. We have characterized empirically the
star-formation "main sequence" (SFMS) and the mass-metallicity relation (MZR)
for this sample, and also identified a class of low-metallicity starbursts,
rare locally but more common in the distant universe. These galaxies deviate
significantly from the main scaling relations, with high SFR and low metal
content for a given M*. In this paper, we model the scaling relations and
explain these deviations from them with a set of multi-phase chemical evolution
models based on the idea that, independently of redshift, initial physical
conditions in a galaxy's evolutionary history can dictate its location in the
scaling relations. Our models are able to successfully reproduce the O/H, M*,
and SFR scaling relations up to z~3, and also successfully predict the
molecular cloud fraction as a function of stellar mass. These results suggest
that the scaling relations are defined by different modes of star formation: an
"active" starburst mode, more common at high redshift, and a quiescent
"passive" mode that is predominant locally and governs the main trends. |
gevolution: a cosmological N-body code based on General Relativity: We present a new N-body code, gevolution, for the evolution of large scale
structure in the Universe. Our code is based on a weak field expansion of
General Relativity and calculates all six metric degrees of freedom in Poisson
gauge. N-body particles are evolved by solving the geodesic equation which we
write in terms of a canonical momentum such that it remains valid also for
relativistic particles. We validate the code by considering the Schwarzschild
solution and, in the Newtonian limit, by comparing with the Newtonian N-body
codes Gadget-2 and RAMSES. We then proceed with a simulation of large scale
structure in a Universe with massive neutrinos where we study the gravitational
slip induced by the neutrino shear stress. The code can be extended to include
different kinds of dark energy or modified gravity models and going beyond the
usually adopted quasi-static approximation. Our code is publicly available. | Host Galaxies of z=4 Quasars: We have undertaken a project to investigate the host galaxies and
environments of a sample of quasars at z~4. In this paper, we describe deep
near-infrared imaging of 34 targets using the Magellan I and Gemini North
telescopes. We discuss in detail special challenges of distortion and
nonlinearity that must be addressed when performing PSF subtraction with data
from these telescopes and their IR cameras, especially in very good seeing. We
derive black hole masses from emission-line spectroscopy, and we calculate
accretion rates from our K_s-band photometry, which directly samples the
rest-frame B for these objects. We introduce a new isophotal diameter technique
for estimating host galaxy luminosities. We report the detection of four host
galaxies on our deepest, sharpest images, and present upper limits for the
others. We find that if host galaxies passively evolve such that they brighten
by 2 magnitudes or more in the rest-frame B band between the present and z=4,
then high-z hosts are less massive at a given black hole mass than are their
low-z counterparts. We argue that the most massive hosts plateau at <~10L*. We
estimate the importance of selection effects on this survey and the subsequent
limitations of our conclusions. These results are in broad agreement with
recent semi-analytical models for the formation of luminous quasars and their
host spheroids by mergers of gas-rich galaxies, with significant dissipation,
and self-regulation of black hole growth and star-formation by the burst of
merger-induced quasar activity. |
Reconstructing Redshift Distributions with Cross-Correlations: Tests and
an Optimized Recipe: Many of the cosmological tests to be performed by planned dark energy
experiments will require extremely well-characterized photometric redshift
measurements. Current estimates are that the true mean redshift of the objects
in each photo-z bin must be known to better than 0.002(1+z) if errors in
cosmological measurements are not to be degraded. A conventional approach is to
calibrate these photometric redshifts with large sets of spectroscopic
redshifts. However, at the depths probed by Stage III surveys (such as DES),
let alone Stage IV (LSST, JDEM, Euclid), existing large redshift samples have
all been highly (25-60%) incomplete. A powerful alternative approach is to
exploit the clustering of galaxies to perform photometric redshift
calibrations. Measuring the two-point angular cross-correlation between objects
in some photometric redshift bin and objects with known spectroscopic redshift
allows the true redshift distribution of a photometric sample to be
reconstructed in detail, even if it includes objects too faint for spectroscopy
or if spectroscopic samples are highly incomplete. We test this technique using
mock DEEP2 Galaxy Redshift survey light cones constructed from the Millennium
Simulation semi-analytic galaxy catalogs. From this realistic test, we find
that the true redshift distribution of a photometric sample can, in fact, be
determined accurately with cross-correlation techniques. We also compare the
empirical error in the reconstruction of redshift distributions to previous
analytic predictions, finding that additional components must be included in
error budgets to match the simulation results. We conclude by presenting a
step-by-step, optimized recipe for reconstructing redshift distributions using
standard correlation measurements. | Lensing and time-delay contributions to galaxy correlations: Galaxy clustering on very large scales can be probed via the 2-point
correlation function in the general case of wide and deep separations,
including all the lightcone and relativistic effects. Using our recently
developed formalism, we analyze the behavior of the local and integrated
contributions and how these depend on redshift range, linear and angular
separations and luminosity function. Relativistic corrections to the local part
of the correlation can be non-negligible but they remain generally
sub-dominant. On the other hand, the additional correlations arising from
lensing convergence and time-delay effects can become very important and even
dominate the observed total correlation function. We investigate different
configurations formed by the observer and the pair of galaxies, and we find
that the case of near-radial large-scale separations is where these effects
will be the most important. |
Through Thick and Thin - HI Absorption in Cosmological Simulations: We investigate the column density distribution function of neutral hydrogen
at redshift z = 3 using a cosmological simulation of galaxy formation from the
OverWhelmingly Large Simulations (OWLS) project. The base simulation includes
gravity, hydrodynamics, star formation, supernovae feedback, stellar winds,
chemodynamics, and element-by-element cooling in the presence of a uniform UV
background. Self-shielding and formation of molecular hydrogen are treated in
post-processing, without introducing any free parameters, using an accurate
reverse ray-tracing algorithm and an empirical relation between gas pressure
and molecular mass fraction. The simulation reproduces the observed z = 3
abundance of Ly-A forest, Lyman Limit and Damped Ly-A HI absorption systems
probed by quasar sight lines over ten orders of magnitude in column density.
Self-shielding flattens the column density distribution for NHI > 10^18 cm-2,
while the conversion to fully neutral gas and conversion of HI to H2 steepen it
around column densities of NHI = 10^20.3 cm-2 and NHI = 10^21.5 cm-2,
respectively. | Cosmological parameters from lenses distance ratio: Strong lensing provides popular techniques to investigate the mass
distribution of intermediate redshift galaxies, testing galaxy evolution and
formation scenarios. It especially probes the background cosmic expansion,
hence constraining cosmological parameters. The measurement of Einstein radii
and central velocity dispersions indeed allows to trace the ratio D_s/D_ls
between the distance D_s from the observer to the source and the distance D_ls
from the lens to the source. We present an improved method to explicitly
include the two - component structure in the galaxy lens modeling, in order to
analyze the role played by the redshift and the model dependence on a nuisance
parameter, F_E, which is usually marginalized in the cosmological applications.
We show how to deal with these problems and carry on a Fisher matrix analysis
to infer the accuracy on cosmological parameters achieved by this method. |
The Atacama Cosmology Telescope: Calibration with WMAP Using
Cross-Correlations: We present a new calibration method based on cross-correlations with WMAP and
apply it to data from the Atacama Cosmology Telescope (ACT). ACT's observing
strategy and map making procedure allows an unbiased reconstruction of the
modes in the maps over a wide range of multipoles. By directly matching the ACT
maps to WMAP observations in the multipole range of 400 < ell < 1000, we
determine the absolute calibration with an uncertainty of 2% in temperature.
The precise measurement of the calibration error directly impacts the
uncertainties in the cosmological parameters estimated from the ACT power
spectra. We also present a combined map based on ACT and WMAP data that has
high signal-to-noise over a wide range of multipoles. | Massive gravity, the elasticity of space-time and perturbations in the
dark sector: We consider a class of modified gravity models where the terms added to the
standard Einstein-Hilbert Lagrangian are just a function of the metric only.
For linearized perturbations around an isotropic space-time, this class of
models is entirely specified by a rank 4 tensor that encodes possibly
time-dependent masses for the gravitons. This tensor has the same symmetries as
an elasticity tensor, suggesting an interpretation of massive gravity as an
effective rigidity of space-time. If we choose a form for this tensor which is
compatible with the symmetries of FRW and enforce full reparameterization
invariance, then the only theory possible is a cosmological constant. However,
in the case where the theory is only time translation invariant, the ghost-free
massive gravity theory is equivalent to the elastic dark energy scenario with
the extra Lorentz violating vector giving rise to 2 transverse and 1
longitudinal degrees of freedom, whereas when one demands spatial translation
invariance one is left with scalar field theory with a non-standard kinetic
term. |
Aspherical ULDM Collapse: Variation in the Core-Halo Mass Relation: Ultralight dark matter (ULDM) is an interesting alternative to the cold dark
matter (CDM) paradigm. Due to the extremely low mass of the constituent
particle ($\sim 10^{-22}$ eV), ULDM can exhibit quantum effects up to
kiloparsec scales. In particular, runaway collapse in the centres of ULDM halos
is prevented by quantum pressure, providing a possible resolution to the
'core-cusp problem' of CDM. However, the the detailed relationship between the
ULDM core mass and that of the overall halo is poorly understood. We simulate
the collapse of both spherical and aspherical isolated ULDM overdensities using
AxioNyx, finding that the central cores of collapsed halos undergo sustained
oscillatory behaviour which affects both their peak density and overall
morphology. The variability in core morphology increases with the asphericity
of the initial overdensity and remnants of initial asphericity persist long
after collapse. Furthermore, the peak central densities are higher in spherical
configurations. Consequently, astrophysically realistic halos may exhibit
substantial departures from theoretical core-halo profiles and we would expect
a significant variance of the properties of halos with the same mass. | Near-IR Integral Field Spectroscopy study of the Star Formation and AGN
of the LIRG NGC 5135: We present a study of the central 2.3 kpc of NGC 5135, a nearby Luminous
Infrared Galaxy (LIRG) with an AGN and circumnuclear starburst. Our main
results are based on intermediate spectral resolution (~ 3000-4000) near
infrared data taken with the SINFONI integral field spectrograph at the ESO
VLT. The ionization of the different phases of the interstellar gas and the
complex structures of the star formation have been mapped. Individual regions
of interest have been identified and studied in detail.
For the first time in this galaxy, we have detected the presence of a high
excitation ionization cone centered on the AGN by using the [SiVI] (1.96
micron) line. So far, this structure is the largest reported in the literature
for this coronal line, extending (in projection) as far as ~ 600 pc from the
galaxy nucleus. In a complex spatial distribution, a variety of mechanisms are
driving the gas ionization, including SNe remnant shocks, young stars and AGN
photoionization. The excitation of the molecular gas, however, is mainly
produced by X-rays and SNe remnant shocks. UV-mechanisms like fluorescence
represent a marginal overall contribution to this process, contrary to the
expectations we might have for a galaxy with a recent and strong star
formation. Our SNe rate estimations from [FeII] (1.64 micron) are in excellent
agreement with 6 cm radio emission predictions. Typical SNe rates between
0.01-0.04 yr^-1 were found for individual ~ 200 pc-scale regions, with an
overall SNe rate of 0.4-0.5 yr^-1. Even though NGC 5135 has suffered a recent
starburst (6-7 Myr ago), the data strongly suggest the presence of a second,
older stellar population dominated by red giant/supergiant stars. |
Signatures of Velocity-Dependent Dark Matter Self-Interactions in Milky
Way-mass Halos: We explore the impact of elastic, anisotropic, velocity-dependent dark matter
(DM) self-interactions on the host halo and subhalos of Milky Way (MW)--mass
systems. We consider a generic self-interacting dark matter (SIDM) model
parameterized by the masses of a light mediator and the DM particle. The ratio
of these masses, $w$, sets the velocity scale above which momentum transfer due
to DM self-interactions becomes inefficient. We perform high-resolution zoom-in
simulations of an MW-mass halo for values of $w$ that span scenarios in which
self-interactions either between the host and its subhalos or only within
subhalos efficiently transfer momentum, and we study the effects of
self-interactions on the host halo and on the abundance, radial distribution,
orbital dynamics, and density profiles of subhalos in each case. The abundance
and properties of surviving subhalos are consistent with being determined
primarily by subhalo--host halo interactions. In particular, subhalos on radial
orbits in models with larger values of the cross section at the host halo
velocity scale are more susceptible to tidal disruption owing to mass loss from
ram pressure stripping caused by self-interactions with the host. This
mechanism suppresses the abundance of surviving subhalos relative to
collisionless DM simulations, with stronger suppression for larger values of
$w$. Thus, probes of subhalo abundance around MW-mass hosts can be used to
place upper limits on the self-interaction cross section at velocity scales of
$\sim 200\ \rm{km\ s}^{-1}$, and combining these measurements with the orbital
properties and internal dynamics of subhalos may break degeneracies among
velocity-dependent SIDM models. | Compton-thick active galactic nuclei inside local ultraluminous infrared
galaxies: We present the X-ray analysis of the most luminous obscured active galactic
nuclei (AGN) inside local ultraluminous infrared galaxies (ULIRGs). Our sample
consists of ten sources, harbouring AGN components with estimated luminosity in
excess of ~10^12 L_sun and yet unidentified at optical wavelengths because of
their large obscuration. According to the Chandra and XMM-Newton spectra, only
in two cases out of ten clear AGN signatures are detected at 2-10 keV in the
shape of reflected emission. The X-ray flux from the starburst (SB) components,
instead, is always broadly consistent with the expectations based on their IR
emission. The most convincing explanation for the missing AGN detections is
therefore the Compton-thickness of the X-ray absorber. In general, the
combination of our mid-IR and X-ray spectral analysis suggests that the
environment surrounding the AGN component in ULIRGs is much richer in gas and
dust than in ordinary active galaxies, and the degree of AGN absorption can be
tentatively related to the SB intensity, indicating a strong interaction
between the two processes and supporting the ULIRG/quasar evolutionary scheme. |
Early publications about nonzero cosmological constant: In 2011 the Nobel Prize in Physics was awarded for the 1998 discovery of the
nonzero cosmological constant. This discovery is very important and surely
worth to receive the Nobel Prize. However, years earlier several papers had
been published (Paal, Horvath, & Lukacs 1992; Holba et al. 1992, Holba et al.
1994) about a very similar discovery from observational data. | Radio Weak Gravitational Lensing with VLA and MERLIN: We carry out an exploratory weak gravitational lensing analysis on a combined
VLA and MERLIN radio data set: a deep (3.3 micro-Jy beam^-1 rms noise) 1.4 GHz
image of the Hubble Deep Field North. We measure the shear estimator
distribution at this radio sensitivity for the first time, finding a similar
distribution to that of optical shear estimators for HST ACS data in this
field. We examine the residual systematics in shear estimation for the radio
data, and give cosmological constraints from radio-optical shear
cross-correlation functions. We emphasize the utility of cross-correlating
shear estimators from radio and optical data in order to reduce the impact of
systematics. Unexpectedly we find no evidence of correlation between optical
and radio intrinsic ellipticities of matched objects; this result improves the
properties of optical-radio lensing cross-correlations. We explore the
ellipticity distribution of the radio counterparts to optical sources
statistically, confirming the lack of correlation; as a result we suggest a
connected statistical approach to radio shear measurements. |
Non-minimally coupled f(R) Cosmology: We investigate the consequences of non-minimal gravitational coupling to
matter and study how it differs from the case of minimal coupling by choosing
certain simple forms for the nature of coupling, The values of the parameters
are specified at $z=0$ (present epoch) and the equations are evolved backwards
to calculate the evolution of cosmological parameters. We find that the Hubble
parameter evolves more slowly in non-minimal coupling case as compared to the
minimal coupling case. In both the cases, the universe accelerates around
present time, and enters the decelerating regime in the past. Using the latest
Union2 dataset for supernova Type Ia observations as well as the data for
baryon acoustic oscillation (BAO) from SDSS observations, we constraint the
parameters of Linder exponential model in the two different approaches. We find
that there is a upper bound on model parameter in minimal coupling. But for
non-minimal coupling case, there is range of allowed values for the model
parameter. | Physical conditions in the ISM of intensely star-forming galaxies at
redshift~2: We analyze the physical conditions in the interstellar gas of 11 actively
star-forming galaxies at z~2, based on integral-field spectroscopy from the
ESO-VLT and HST/NICMOS imaging. We concentrate on the high H-alpha surface
brightnesses, large line widths, line ratios and the clumpy nature of these
galaxies. We show that photoionization calculations and emission line
diagnostics imply gas pressures and densities that are similar to the most
intense nearby star-forming regions at z=0 but over much larger scales (10-20
kpc). A relationship between surface brightness and velocity dispersion can be
explained through simple energy injection arguments and a scaling set by nearby
galaxies with no free parameters. The high velocity dispersions are a natural
consequence of intense star formation thus regions of high velocity dispersion
are not evidence for mass concentrations such as bulges or rings. External
mechanisms like cosmological gas accretion generally do not have enough energy
to sustain the high velocity dispersions. In some cases, the high pressures and
low gas metallicites may make it difficult to robustly distinguish between AGN
ionization cones and star formation, as we show for BzK-15504 at z=2.38. We
construct a picture where the early stages of galaxy evolution are driven by
self-gravity which powers strong turbulence until the velocity dispersion is
high. Then massive, dense, gas-rich clumps collapse, triggering star formation
with high efficiencies and intensities as observed. At this stage, the intense
star formation is likely self-regulated by the mechanical energy output of
massive stars. |
Inferring galaxy cluster masses from cosmic microwave background lensing
with neural simulation based inference: Gravitational lensing by massive galaxy clusters distorts the observed cosmic
microwave background (CMB) on arcminute scales, and these distortions carry
information about cluster masses. Standard approaches to extracting cluster
mass constraints from the CMB cluster lensing signal are either sub-optimal,
ignore important physical or observational effects, are computationally
intractable, or require additional work to turn the lensing measurements into
constraints on cluster masses. We apply simulation based inference (SBI) using
neural likelihood models to the problem. We show that in circumstances where
the exact likelihood can be computed, the SBI constraints on cluster masses are
in agreement with the exact likelihood, demonstrating that the SBI constraints
are close to optimal. In scenarios where the exact likelihood cannot be
feasibly computed, SBI still recovers unbiased estimates of individual cluster
masses and combined constraints from multiple clusters. SBI will be a powerful
tool for constraining the masses of galaxy clusters detected by future cosmic
surveys. Code to run the analyses presented here will be made publicly
available. | Dark Energy in vector-tensor theories of gravity: We consider a general class of vector-tensor theories of gravity and show
that solutions with accelerated expansion and a future type III singularity are
a common feature in these models. We also show that there are only six
vector-tensor theories with the same small scales behavior as General
Relativity and, in addition, only two of them can be made completely free from
instabilities. Finally, two particular models as candidates for dark energy are
proposed: on one hand, a cosmic vector that allows to alleviate the usual
naturalness and coincidence problems and, on the other hand, the
electromagnetic field is shown to give rise to an effective cosmological
constant on large scales whose value can be explained in terms of inflation at
the electroweak scale. |
ALFALFA HI Content and Star Formation in Virgo Cluster Early-Type Dwarfs: The ALFALFA (Arecibo Legacy Fast ALFA) blind survey is providing a census of
HI in galaxies of all types in a range of environments. Here we report on
ALFALFA results for Virgo Cluster early-type dwarfs between declinations of 4
and 16 degrees. Less than 2% of the Virgo early-type dwarf population is
detected, compared to 70-80% of the Im/BCD dwarf population. Most of the dwarfs
detected in HI show evidence for ongoing or recent star formation. Early-type
galaxies with HI tend to be located in the outer regions of the cluster and to
be brighter. Early-type dwarfs with HI may be undergoing morphological
transition due to cluster environmental effects. | Statistics of Inflating Regions in Eternal Inflation: We compute the distribution of sizes of inflating and non-inflating regions
in an eternally inflating Universe. As a first illustrative problem, we study a
simple scenario of an eternally inflating Universe in the presence of a
massless scalar field $\varphi$ whose field values lie within some finite
domain $\varphi\in(-\varphi_{cr},\varphi_{cr})$, with $\pm\varphi_{cr}$ marking
the onset of thermalization/crunching. We compute many important quantities,
including the fractal dimension, distribution of field values among inflating
regions, and the number of inflating and non-inflating Hubble regions. With the
aid of simulations in 1 spatial dimension, we show this eternally inflating
Universe reaches a steady state in which average sizes of inflating regions
grow only as a power law in the field's crunch value $\sim \varphi_{cr}^2$
(extension to higher dimensions is $\sim\varphi^{2/D}$), contrary to a naive
expectation of an exponential dependence. Furthermore, the distribution in
sizes exhibits an exponential fall off for large distances (with an initial
power law for inflating regions). We leave other interesting cases of more
realistic potentials and time varying Hubble parameter for future work, with a
possible application to the SM Higgs in the early Universe. |
Probing the circumgalactic medium with CMB polarization statistical
anisotropy: As cosmic microwave background (CMB) photons traverse the Universe,
anisotropies can be induced via Thomson scattering (proportional to the
integrated electron density; optical depth) and inverse Compton scattering
(proportional to the integrated electron pressure; thermal Sunyaev-Zel'dovich
effect). Measurements of anisotropy in optical depth $\tau$ and Compton $y$
parameter are imprinted by the galaxies and galaxy clusters and are thus
sensitive to the thermodynamic properties of circumgalactic medium and
intergalactic medium. We use an analytic halo model to predict the power
spectrum of the optical depth ($\tau\tau$), the cross-correlation between the
optical depth and the Compton $y$ parameter ($\tau y$), as well as the
cross-correlation between the optical depth and galaxy clustering ($\tau g$),
and compare this model to cosmological simulations. We constrain the optical
depths of halos at $z\lesssim 3$ using a technique originally devised to
constrain patchy reionization at a much higher redshift range. The forecasted
signal-to-noise ratio is 2.6, 8.5, and 13, respectively, for a CMB-S4-like
experiment and a VRO-like optical survey. We show that a joint analysis of
these probes can constrain the amplitude of the density profiles of halos to
6.5% and the pressure profile to 13%, marginalizing over the outer slope of the
pressure profile. These constraints translate to astrophysical parameters
related to the physics of galaxy evolution, such as the gas mass fraction,
$f_{\rm g}$, which can be constrained to 5.3% uncertainty at $z\sim 0$,
assuming an underlying model for the shape of the density profile. The
cross-correlations presented here are complementary to other CMB and galaxy
cross-correlations since they do not require spectroscopic galaxy redshifts and
are another example of how such correlations are a powerful probe of the
astrophysics of galaxy evolution. | The Arizona CDFS Environment Survey (ACES): A Magellan/IMACS
Spectroscopic Survey of the Chandra Deep Field South: We present the Arizona CDFS Environment Survey (ACES), a recently-completed
spectroscopic redshift survey of the Chandra Deep Field South (CDFS) conducted
using IMACS on the Magellan-Baade telescope. In total, the survey targeted 7277
unique sources down to a limiting magnitude of R = 24.1, yielding 5080 secure
redshifts across the ~30' x 30' extended CDFS region. The ACES dataset delivers
a significant increase to both the spatial coverage and the sampling density of
the spectroscopic observations in the field. Combined with
previously-published, spectroscopic redshifts, ACES now creates a
highly-complete survey of the galaxy population at R < 23, enabling the local
galaxy density (or environment) on relatively small scales (~1 Mpc) to be
measured at z < 1 in one of the most heavily-studied and data-rich fields in
the sky. Here, we describe the motivation, design, and implementation of the
survey and present a preliminary redshift and environment catalog. In addition,
we utilize the ACES spectroscopic redshift catalog to assess the quality of
photometric redshifts from both the COMBO-17 and MUSYC imaging surveys of the
CDFS. |
Light/Mass Offsets in the Lensing Cluster Abell 3827: Evidence for
Collisional Dark Matter?: If dark matter has a non-zero self-interaction cross-section, then dark
matter halos of individual galaxies in cluster cores should experience a drag
force from the ambient dark matter of the cluster, which will not affect the
stellar components of galaxies, and thus will lead to a separation between the
stellar and dark matter. If the cross-section is only a few decades below its
current astrophysically determined upper limit, then kpc-scale separations
should result. However, such separations will be observable only under very
favorable conditions. Abell 3827 is a nearby late stage cluster merger with
four massive central ellipticals within 20 kpc of each other. The ten strong
lensing images tightly surrounding the ellipticals provide an excellent set of
constraints for a free-form lens reconstruction. Our free-form mass maps show a
massive dark extended clump, about 6 kpc from one of the ellipticals. The
robustness of this result has been tested with many reconstructions, and
confirmed with experiments using synthetic lens mass distributions. Interpreted
in terms of dark matter collisionality, our result yields sigma/m ~ 4.5 10^{-7}
(t/10^{10} yr)^{-2} cm^2/g, where t is the merger's age. | How do dwarf galaxies acquire their mass & when do they form their
stars?: We apply a simple, one-equation, galaxy formation model on top of the halos
and subhalos of a high-resolution dark matter cosmological simulation to study
how dwarf galaxies acquire their mass and, for better mass resolution, on over
10^5 halo merger trees, to predict when they form their stars. With the first
approach, we show that the large majority of galaxies within group- and
cluster-mass halos have acquired the bulk of their stellar mass through gas
accretion and not via galaxy mergers. We deduce that most dwarf ellipticals are
not built up by galaxy mergers. With the second approach, we constrain the star
formation histories of dwarfs by requiring that star formation must occur
within halos of a minimum circular velocity set by the evolution of the
temperature of the IGM, starting before the epoch of reionization. We
qualitatively reproduce the downsizing trend of greater ages at greater masses
and predict an upsizing trend of greater ages as one proceeds to masses lower
than m_crit. We find that the fraction of galaxies with very young stellar
populations (more than half the mass formed within the last 1.5 Gyr) is a
function of present-day mass in stars and cold gas, which peaks at 0.5% at
m_crit=10^6-8 M_Sun, corresponding to blue compact dwarfs such as I Zw 18. We
predict that the baryonic mass function of galaxies should not show a maximum
at masses above 10^5.5, M_Sun, and we speculate on the nature of the lowest
mass galaxies. |
Measuring our velocity from fluctuations in number counts: Our velocity relative to the cosmic microwave background (CMB) generates a
dipole from the CMB monopole, which was accurately measured by COBE. The
relative velocity also modulates and aberrates the CMB fluctuations, generating
a small signature of statistical isotropy violation in the covariance matrix.
This signature was first measured by Planck 2013. Galaxy surveys are similarly
affected by a Doppler boost. The dipole generated from the number count
monopole has been extensively discussed, and measured (at very low accuracy) in
the NVSS and TGSS radio continuum surveys. For the first time, we present an
analysis of the Doppler imprint on the number count fluctuations, using the
bipolar spherical harmonic formalism to quantify these effects. Next-generation
wide-area surveys with a high redshift range are needed to detect the small
Doppler signature in number count fluctuations. We show that radio continuum
surveys with the SKA should enable a detection at $\gtrsim 3 \sigma$ in Phase
2, with marginal detection possible in Phase 1. | Constraints on Cosmological Parameters with a Sample of Type Ia
Supernovae from JWST: We investigate the potential of using a sample of very high-redshift
($2\lesssim z \lesssim6$) (VHZ) Type Ia supernovae (SNe~Ia) attainable by the
James Webb Space Telescope (JWST) on constraining cosmological parameters. At
such high redshifts, the age of the universe is young enough that the VHZ SNIa
sample comprises the very first SNe~Ia of the universe, with progenitors among
the very first generation of low mass stars that the universe has made. We show
that the VHZ SNe~Ia can be used to disentangle systematic effects due to the
luminosity distance evolution with redshifts intrinsic to SNIa standardization.
Assuming that the systematic evolution can be described by a linear or
logarithmic formula, we found that the coefficients of this dependence can be
determined accurately and decoupled from cosmological models. Systematic
evolution as large as 0.15 mag and 0.45 mag out to $z=5$ can be robustly
separated from popular cosmological models for the linear and logarithmic
evolution, respectively. The VHZ SNe~Ia will lay the foundation for quantifying
the systematic redshift evolution of SNIa luminosity distance scales. When
combined with SNIa surveys at comparatively lower redshifts, the VHZ SNe~Ia
allow for a precise measurement of the history of the expansion of the universe
from $z\sim 0$ to the epoch approaching reionization. |
Spitzer IRS 16 micron Observations of the GOODS Fields: We present Spitzer 16 micron imaging of the Great Observatories Origins Deep
Survey (GOODS) fields. We survey 150 square arcminutes in each of the two GOODS
fields (North and South), to an average 3 sigma depth of 40 and 65 micro-Jy
respectively. We detect about 1300 sources in both fields combined. We validate
the photometry using the 3-24 micron spectral energy distribution of stars in
the fields compared to Spitzer spectroscopic templates. Comparison with ISOCAM
and AKARI observations in the same fields show reasonable agreement, though the
uncertainties are large. We provide a catalog of photometry, with sources cross
correlated with available Spitzer, Chandra, and HST data. Galaxy number counts
show good agreement with previous results from ISOCAM and AKARI, with improved
uncertainties. We examine the 16 to 24 micron flux ratio and find that for most
sources it lies within the expected locus for starbursts and infrared luminous
galaxies. A color cut of S_{16}/S_{24}>1.4 selects mostly sources which lie at
1.1<z<1.6, where the 24 micron passband contains both the redshifted 9.7 micron
silicate absorption and the minimum between PAH emission peaks. We measure the
integrated galaxy light of 16 micron sources, and find a lower limit on the
galaxy contribution to the extragalactic background light at this wavelength to
be 2.2\pm 0.2$ nW m^{-2} sr^{-1}. | Lookback time and Chandra constrains on cosmological parameters: In this paper we combine the WMAP7 with lookback time and Chandra gas
fraction data to constrain the main cosmological parameters and the equation of
state for the dark energy. We find that the lookback time is a good measurement
that can improve the determination of the equation of state for the dark energy
with regard to other external data sets. We conclude that larger lookback time
data set will further improve our determination of the cosmological parameters. |
The relation between metallicity, stellar mass and star formation in
galaxies: an analysis of observational and model data: We study relations between stellar mass, star formation and gas-phase
metallicity in a sample of 177,071 unique emission line galaxies from the
SDSS-DR7, as well as in a sample of 43,767 star forming galaxies at z=0 from
the cosmological semi-analytic model L-GALAXIES. We demonstrate that
metallicity is dependent on star formation rate at fixed mass, but that the
trend is opposite for low and for high mass galaxies. Low-mass galaxies that
are actively forming stars are more metal-poor than quiescent low-mass
galaxies. High-mass galaxies, on the other hand, have lower gas-phase
metallicities if their star formation rates are small. Remarkably, the same
trends are found for our sample of model galaxies. We find that massive model
galaxies with low gas-phase metallicities have undergone a gas-rich merger in
the past, inducing a starburst which exhausted their cold gas reservoirs and
shut down star formation. This led to a gradual dilution in the gas-phase
metallicities of these systems via accretion of gas. These model galaxies have
lower-than-average gas-to-stellar mass ratios and higher-than-average central
black hole masses. We confirm that massive galaxies with low gas-phase
metallicities in our observational sample also have very massive black holes.
We propose that accretion may therefore play a significant role in regulating
the gas-phase metallicities of present-day massive galaxies. | Emergent Universe from Scale Invariant Two Measures Theory: The dilaton-gravity sector of a linear in the scalar curvature, scale
invariant Two Measures Field Theory (TMT), is explored in detail in the context
of closed FRW cosmology and shown to allow stable emerging universe solutions.
The model possesses scale invariance which is spontaneously broken due to the
intrinsic features of the TMT dynamics. We study the transition from the
emerging phase to inflation, and then to a zero cosmological constant phase. We
also study the spectrum of density perturbations and the constraints that
impose on the parameters of the theory. |
Sharp turns in axion monodromy: primordial black holes and gravitational
waves: Large turns in multifield inflation can lead to a very rich phenomenology,
but are difficult to realise in supergravity, and typically require large field
space curvatures. In this work, we present a mechanism to realise multiple
sharp turns, and therefore strong non-geodesic trajectories, from transient
violations of slow-roll without the requirement of large field space curvatures
in supergravity inflation. Such turning rates can strongly source the adiabatic
fluctuations, resulting in an enhanced scalar power spectrum with resonant
features and a large peak amplitude. If the growth of the scalar power spectrum
at small scales is large enough, primordial black holes can be produced in
abundance. These large scalar fluctuations induce a characteristic large
spectrum of gravitational waves for a wide range of frequencies, which inherits
the resonant features. We illustrate this mechanism in a supergravity model of
axion monodromy, which provides the first concrete model to realise such
resonant features. The model can sustain inflation for around 60 e-folds,
leading to considerable production of very light primordial black holes, and
large gravitational wave spectra, which could be detectable by multiple
upcoming gravitational wave surveys. For the set of parameter we consider,
large oscillations occur at all scales. This represents a challenge for the
model at large scales and motivates further investigation to reconcile this
class of models with Planck data. | Quasar host galaxies in the SDSS Stripe 82: We present first results from our study of the properties of ~400 low
redshift (z < 0.5) quasars, based on a large homogeneous dataset derived from
the Stripe 82 area of the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7).
For this sky region, deep (r~22.4) u,g,r,i,z images are available, up to ~2 mag
deeper than standard SDSS images, allowing us to study both the host galaxies
and the Mpc-scale environments of the quasars. This sample greatly outnumbers
previous studies of low redshift quasar hosts, from the ground or from space.
Here we report the preliminary results for the quasar host galaxies. We are
able to resolve the host galaxy in ~80 % of the quasars. The quasar hosts are
luminous and large, the majority of them in the range between M*-1 and M*-2,
and with ~10 kpc galaxy scale-lengths. Almost half of the host galaxies are
best fit with an exponential disk, while the rest are spheroid-dominated. There
is a reasonable relation between the central black hole mass and the host
galaxy luminosity. |
Dark Photon Dark Matter in the Presence of Inhomogeneous Structure: Dark photon dark matter will resonantly convert into visible photons when the
dark photon mass is equal to the plasma frequency of the ambient medium. In
cosmological contexts, this transition leads to an extremely efficient, albeit
short-lived, heating of the surrounding gas. Existing work in this field has
been predominantly focused on understanding the implications of these resonant
transitions in the limit that the plasma frequency of the Universe can be
treated as being perfectly homogeneous, \ie neglecting inhomogeneities in the
electron number density. In this work we focus on the implications of heating
from dark photon dark matter in the presence of inhomogeneous structure (which
is particularly relevant for dark photons with masses in the range $10^{-15} \,
{\rm eV} \, \lesssim m_{A^\prime} \lesssim 10^{-12}$ eV), emphasizing both the
importance of inhomogeneous energy injection, as well as the sensitivity of
cosmological observations to the inhomogeneities themselves. More specifically,
we derive modified constraints on dark photon dark matter from the Ly-$\alpha$
forest, and show that the presence of inhomogeneities allows one to extend
constraints to masses outside of the range that would be obtainable in the
homogeneous limit, while only slightly relaxing their strength. We then project
sensitivity for near-future cosmological surveys that are hoping to measure the
21cm transition in neutral hydrogen prior to reionization, and demonstrate that
these experiments will be extremely useful in improving sensitivity to masses
near $\sim 10^{-14}$ eV, potentially by several orders of magnitude. Finally,
we discuss implications for reionization, early star formation, and late-time
$y$-type spectral distortions, and show that probes which are inherently
sensitive to the inhomogeneous state of the Universe could resolve signatures
unique to the light dark photon... | Selecting background galaxies in weak-lensing analysis of galaxy
clusters: In this paper, we present a new method to select the faint, background
galaxies used to derive the mass of galaxy clusters by weak lensing.
The method is based on the simultaneous analysis of the shear signal, that
should be consistent with zero for the foreground, unlensed galaxies, and of
the colors of the galaxies: photometric data from the COSMic evOlution Survey
are used to train the color selection. In order to validate this methodology,
we test it against a set of state-of-the-art image simulations of mock galaxy
clusters in different redshift [$0.23-0.45$] and mass
[$0.5-1.55\times10^{15}M_\odot$] ranges, mimicking medium-deep multicolor
imaging observations (e.g. SUBARU, LBT).
The performance of our method in terms of contamination by unlensed sources
is comparable to a selection based on photometric redshifts, which however
requires a good spectral coverage and is thus much more observationally
demanding. The application of our method to simulations gives an average ratio
between estimated and true masses of $\sim 0.98 \pm 0.09$. As a further test,
we finally apply our method to real data, and compare our results with other
weak lensing mass estimates in the literature: for this purpose we choose the
cluster Abell 2219 ($z=0.228$), for which multi-band (BVRi) data are publicly
available. |
The XXL survey: XLII. Detection and characterization of the galaxy
population of distant galaxy clusters in the XXL-N/VIDEO field: A tale of
variety: Context. Distant galaxy clusters provide an effective laboratory in which to
study galaxy evolution in dense environments and at early cosmic times. Aims.
We aim to identify distant galaxy clusters as extended X-ray sources coincident
with overdensities of characteristically bright galaxies. Methods. We use
optical and near-infrared (NIR) data from the Hyper Suprime-Cam (HSC) and VISTA
Deep Extragalactic Observations (VIDEO) surveys to identify distant galaxy
clusters as overdensities of bright, $z_{phot}\geq 0.8$ galaxies associated
with extended X-ray sources detected in the ultimate XMM extragalactic survey
(XXL). Results. We identify a sample of 35 candidate clusters at $0.80\leq
z\leq 1.93$ from an approximately 4.5 deg$^2$ sky area. This sample includes 15
newly discovered candidate clusters, ten previously detected but unconfirmed
clusters, and ten spectroscopically confirmed clusters. Although these clusters
host galaxy populations that display a wide variety of quenching levels, they
exhibit well-defined relations between quenching, cluster-centric distance, and
galaxy luminosity. The brightest cluster galaxies (BCGs) within our sample
display colours consistent with a bimodal population composed of an old and red
subsample together with a bluer, more diverse subsample. Conclusions. The
relation between galaxy masses and quenching seem to be already in place at
$z\sim 1$, although there is no significant variation of the quenching fraction
with the cluster-centric radius. The BCG bimodality might be explained by the
presence of a younger stellar component in some BCGs but additional data are
needed to confirm this scenario. | A hybrid simulation of gravitational wave production in first-order
phase transitions: The LISA telescope will provide the first opportunity to probe the scenario
of a first-order phase transition happening close to the electroweak scale. By
now, it is evident that the main contribution to the GW spectrum comes from the
sound waves propagating through the plasma. Current estimates of the GW
spectrum are based on numerical simulations of a scalar field interacting with
the plasma or on analytical approximations -- the so-called sound shell model.
In this work we present a novel setup to calculate the GW spectra from sound
waves. We use a hybrid method that uses a 1d simulation (with spherical
symmetry) to evolve the velocity and enthalpy profiles of a single bubble after
collision and embed it in a 3d realization of multiple bubble collisions,
assuming linear superposition of the velocity and enthalpy. The main advantage
of our method compared to 3d hydrodynamic simulations is that it does not
require to resolve the scale of bubble wall thickness. This makes our
simulations more economical and the only two relevant physical length scales
that enter are the bubble size and the shell thickness (that are in turn
enclosed by the box size and the grid spacing). The reduced costs allow for
extensive parameter studies and we provide a parametrization of the final GW
spectrum as a function of the wall velocity and the fluid kinetic energy. |
Observational tests of inflation with a field derivative coupling to
gravity: A field kinetic coupling with the Einstein tensor leads to a gravitationally
enhanced friction during inflation, by which even steep potentials with
theoretically natural model parameters can drive cosmic acceleration. In the
presence of this non-minimal derivative coupling we place observational
constraints on a number of representative inflationary models such as chaotic
inflation, inflation with exponential potentials, natural inflation, and hybrid
inflation. We show that most of the models can be made compatible with the
current observational data mainly due to the suppressed tensor-to-scalar ratio. | Predicting halo occupation and galaxy assembly bias with machine
learning: Understanding the impact of halo properties beyond halo mass on the
clustering of galaxies (namely galaxy assembly bias) remains a challenge for
contemporary models of galaxy clustering. We explore the use of machine
learning to predict the halo occupations and recover galaxy clustering and
assembly bias in a semi-analytic galaxy formation model. For stellar-mass
selected samples, we train a Random Forest algorithm on the number of central
and satellite galaxies in each dark matter halo. With the predicted
occupations, we create mock galaxy catalogues and measure the clustering and
assembly bias. Using a range of halo and environment properties, we find that
the machine learning predictions of the occupancy variations with secondary
properties, galaxy clustering and assembly bias are all in excellent agreement
with those of our target galaxy formation model. Internal halo properties are
most important for the central galaxies prediction, while environment plays a
critical role for the satellites. Our machine learning models are all provided
in a usable format. We demonstrate that machine learning is a powerful tool for
modelling the galaxy-halo connection, and can be used to create realistic mock
galaxy catalogues which accurately recover the expected occupancy variations,
galaxy clustering and galaxy assembly bias, imperative for cosmological
analyses of upcoming surveys. |
Slowly Breaking Waves: The Longevity of Tidally Induced Spiral Structure: We have discovered long-lived waves in two sets of numerical models of fast
(marginally bound or unbound) flyby galaxy collisions, carried out
independently with two different codes. In neither simulation set are the
spirals the result of a collision-induced bar formation. Although there is
variation in the appearance of the waves with time, they do not disappear and
reform recurrently, as seen in other cases described in the literature. We also
present an analytic theory that can account for the wave structure, not as
propagating transients, nor as a fixed pattern propagating through the disc.
While these waves propagate through the disc, they are maintained by the
coherent oscillations initiated by the impulsive disturbance. Specifically, the
analytic theory suggests that they are caustic waves in ensembles of stars
pursuing correlated epicyclic orbits after the disturbance. This theory is an
extension of that developed by Struck and collaborators for colliding ring
galaxies.
The models suggest that this type of wave may persist for a couple of Gyr.,
and galaxy interactions occur on comparable timescales, so waves produced by
the mechanism may be well represented in observed spirals. In particular, this
mechanism can account for the tightly wound, and presumably long-lived spirals,
seen in some nearby early-type galaxies. These spirals are also likely to be
common in groups and clusters, where fast encounters between galaxies occur
relatively frequently. However, as the spirals become tightly wound, and evolve
to modest amplitudes, they may be difficult to resolve unless they are nearby.
Nonetheless, the effect may be one of several processes that result from galaxy
harassment, and via wave-enhanced star formation contribute to the
Butcher-Oemler effect. | Complex evaluation of angular power spectra: Going beyond the Limber
approximation: Angular power spectra are central to the study of our Universe. In this
paper, I develop a new method for the numeric evaluation and analytic
estimation of the angular cross-power spectrum of two random fields using
complex analysis and Picard- Lefschetz theory. The proposed continuous
deformation of the integration domain resums the highly oscillatory integral
into a convex integral whose integrand decays exponentially. This deformed
integral can be quickly evaluated with conventional integration techniques.
These methods can be used to quickly evaluate and estimate the angular power
spectrum from the three-dimensional power spectrum for all angles (or multipole
moments). This method is especially useful for narrow redshift bins, or samples
with small redshift overlap, for which the Limber approximation has a large
error. |
Skew spectrum and smoothed skewness of 21-cm signals from epoch of
reionization: Due to the non-linear ionizing and heating processes, the 21-cm signals from
epoch of reionization (EoR) are expected to have strong non-Gaussian
fluctuations. In this paper, we use the semi-numerical simulations to study the
non-Gaussian statistics i.e. skew spectrum and smoothed skewness of the 21-cm
signals from EoR. We find the 21-cm skew spectrum and smoothed skewness have
similar evolution features with the 21-cm bispectrum. All of them are sensitive
to the EoR models, while not too much to the cosmic volume applied. With the
SKA1-low telescope as reference, we find both the skew spectrum and smoothed
skewness have much higher S/N ratios than the 21-cm bispectrum. | Secondary infall model and dark matter scaling relations in intermediate
redshift early - type galaxies: Scaling relations among dark matter (DM) and stellar quantities are a
valuable tool to constrain formation scenarios and the evolution of galactic
structures. However, most of the DM properties are actually not directly
measured, but derived through model dependent mass mapping procedures. It is
therefore crucial to adopt theoretically and observationally well founded
models. We use here an updated version of the secondary infall model (SIM) to
predict the halo density profile, taking into account the effects of angular
momentum, dissipative friction and baryons collapse. The resulting family of
halo profiles depends on one parameter only, the virial mass, and nicely fits
the projected mass and aperture velocity dispersion of a sample of intermediate
redshift lens galaxies. We derive DM related quantities (namely the column
density and the Newtonian acceleration) and investigate their correlations with
stellar mass, luminosity, effective radius and virial mass. |
Constraints on the merging channel of massive galaxies since z~1: (Abridged) We probe the merging channel of massive galaxies over the
z=0.3-1.3 redshift window by studying close pairs in a sample of 238 galaxies
with stellar mass >1E11Msun, from the deep (m<26.5AB, 3 sigma) SHARDS survey.
SHARDS provides medium band photometry equivalent to low-resolution optical
spectra (R~50), allowing us to obtain extremely accurate photometric redshifts
(|Dz|/(1+z)~0.55%) and to improve the constraints on the age distribution of
the stellar populations. A strong correlation is found between the age
difference of central and satellite galaxy and stellar mass ratio, from
negligible age differences in major mergers to age differences ~4 Gyr for 1:100
minor mergers. However, this correlation is simply a reflection of the mass-age
trend in the general population. The dominant contributor to the growth of
massive galaxies corresponds to mass ratios mu=Msat/Mcen>0.3, followed by a
decrease in the fractional mass growth rate linearly proportional to log mu, at
least down to mu~0.01, suggesting a decreasing role of mergers involving
low-mass satellites, especially if dynamical friction timescales are taken into
account. A simple model results in an upper limit for the average mass growth
rate of massive galaxies of DM/M/Dt~ 0.08+-0.02 per Gyr, over the z<1 range,
with a ~70% fractional contribution from (major) mergers with mu>0.3. The
majority of the stellar mass contributed by mergers does not introduce
significantly younger populations, in agreement with the small radial age
gradients observed in present-day early-type galaxies. | Setting new Cosmology constraints with ALMA: I make a short revision of Cosmology questions which ALMA was built to
address. Without diving into much detail, I point out the ALMA specifications
and strategies which are expected to provide a better handle of: the
temperature evolution of the Cosmic Microwave Background (CMB) and the
properties of its secondary anisotropies (such as the thermal and kinetic
Sunyaev-Zel'dovich and the Ostriker-Vishniac effects); variability of
dimensionless fundamental constants; Ho and galaxy initial mass function by
means of strong gravitational lensing; black hole science with the greatly
expected Event Horizon Telescope. |
Through the Looking Glass: Why the "Cosmic Horizon" is not a horizon: The present standard model of cosmology, $\Lambda$CDM, contains some
intriguing coincidences. Not only are the dominant contributions to the energy
density approximately of the same order at the present epoch, but we note that
contrary to the emergence of cosmic acceleration as a recent phenomenon, the
time averaged value of the deceleration parameter over the age of the universe
is nearly zero. Curious features like these in $\Lambda$CDM give rise to a
number of alternate cosmologies being proposed to remove them, including models
with an equation of state w = -1/3. In this paper, we examine the validity of
some of these alternate models and we also address some persistent
misconceptions about the Hubble sphere and the event horizon that lead to
erroneous conclusions about cosmology. | Cosmological constraints on Lorentz violating dark energy: The role of Lorentz invariance as a fundamental symmetry of nature has been
lately reconsidered in different approaches to quantum gravity. It is thus
natural to study whether other puzzles of physics may be solved within these
proposals. This may be the case for the cosmological constant problem. Indeed,
it has been shown that breaking Lorentz invariance provides Lagrangians that
can drive the current acceleration of the universe without experiencing large
corrections from ultraviolet physics. In this work, we focus on the simplest
model of this type, called ThetaCDM, and study its cosmological implications in
detail. At the background level, this model cannot be distinguished from
LambdaCDM. The differences appear at the level of perturbations. We show that
in ThetaCDM, the spectrum of CMB anisotropies and matter fluctuations may be
affected by a rescaling of the gravitational constant in the Poisson equation,
by the presence of extra contributions to the anisotropic stress, and finally
by the existence of extra clustering degrees of freedom. To explore these
modifications accurately, we modify the Boltzmann code CLASS. We then use the
parameter inference code Monte Python to confront ThetaCDM with data from
WMAP-7, SPT and WiggleZ. We obtain strong bounds on the parameters accounting
for deviations from LambdaCDM. In particular, we find that the discrepancy
between the gravitational constants appearing in the Poisson and Friedmann
equations is constrained at the level 1.8%. |
Effects of Multi-Field Phantom Inflation in Big Rip: In this paper we study the behavior of the multi-field in phantom inflation,
when massive scalar fields work collectively, in which the scale factor is a
power law. We evaluate its parameter values by applying certain constraints on
our model parameters, and we investigate that before the Big Rip singularity
occurs the universe is in phantom inflationary phase. Furthermore, we calculate
these values for this period then compare with current observations of CMB, BAO
and observational Hubble data. We find that results may be consistent with
observations. This implies that in the dark-energy equation of state (EOS)
parameter $\omega_{DE}$ at the Big Rip remains finite, with the divergence of
pressure and dark energy density. | The large-scale correlations of multi-cell densities and profiles,
implications for cosmic variance estimates: In order to quantify the error budget in the measured probability
distribution functions of cell densities, the two-point statistics of cosmic
densities in concentric spheres is investigated. Bias functions are introduced
as the ratio of their two-point correlation function to the two-point
correlation of the underlying dark matter distribution. They describe how cell
densities are spatially correlated. They are computed here via the so-called
large deviation principle in the quasi-linear regime. Their large-separation
limit is presented and successfully compared to simulations for density and
density slopes: this regime is shown to be rapidly reached allowing to get
sub-percent precision for a wide range of densities and variances. The
corresponding asymptotic limit provides an estimate of the cosmic variance of
standard concentric cell statistics applied to finite surveys. More generally,
no assumption on the separation is required for some specific moments of the
two-point statistics, for instance when predicting the generating function of
cumulants containing any powers of concentric densities in one location and one
power of density at some arbitrary distance from the rest. This exact "one
external leg" cumulant generating function is used in particular to probe the
rate of convergence of the large-separation approximation. |
The merger history of primordial-black-hole binaries: As a candidate of dark matter, primordial black holes (PBHs) have attracted
more and more attentions as they could be possible progenitors of the heavy
binary black holes (BBHs) observed by LIGO/Virgo. Accurately estimating the
merger rate of PBH binaries will be crucial to reconstruct the mass
distribution of PBHs. It was pointed out the merger history of PBHs may shift
the merger rate distribution depending on the mass function of PBHs. In this
paper, we use 10 BBH events from LIGO/Virgo O1 and O2 observing runs to
constrain the merger rate distribution of PBHs by accounting the effect of
merger history. It is found that the second merger process makes subdominant
contribution to the total merger rate, and hence the merger history effect can
be safely neglected. | Recent H.E.S.S. results on extra-galactic sources: Since the beginning of scientific operations in 2003, more than 20
extra-galactic sources have been detected with H.E.S.S. (High Energy
Stereoscopic System) at very high energies (VHE): apart from the starburst
galaxy NGC 253, all of them are active galactic nuclei (AGNs). BL Lac objects
are by far the dominant AGN sub-class in the H.E.S.S. extra-galactic sky, but
two radio-galaxies and one flat-spectrum radio quasar (FSRQ) have been detected
as well. The study of extra-galactic VHE emitters will be improved in the near
future by the completion of a fifth 24m-diameter telescope (H.E.S.S. II). In
this talk, a review of the AGNs seen by H.E.S.S. will be given, including the
latest results achieved, namely the detection of VHE emission from the blazars
1RXS J101015.9-311909, SHBL J001355.9-185406, 1ES 1312-423, AP Lib and the BL
Lac candidate HESS J1943+213. |
Clustering, Cosmology and a New Era of Black Hole Demographics -- I. The
Conditional Luminosity Function of Active Galactic Nuclei: Deep X-ray surveys have provided a comprehensive and largely unbiased view of
active galactic nuclei (AGN) evolution stretching back to $z \sim 5$. However,
it has been challenging to use the survey results to connect this evolution to
the cosmological environment that AGNs inhabit. Exploring this connection will
be crucial to understanding the triggering mechanisms of AGNs and how these
processes manifest in observations at all wavelengths. In anticipation of
upcoming wide-field X-ray surveys that will allow quantitative analysis of AGN
environments, this paper presents a method to observationally constrain the
Conditional Luminosity Function (CLF) of AGNs at a specific $z$. Once measured,
the CLF allows the calculation of the AGN bias, mean dark matter halo mass, AGN
lifetime, halo occupation number, and AGN correlation function -- all as a
function of luminosity. The CLF can be constrained using a measurement of the
X-ray luminosity function and the correlation length at different luminosities.
The method is illustrated at $z \approx 0$ and $0.9$ using the limited data
that is currently available, and a clear luminosity dependence in the AGN bias
and mean halo mass is predicted at both $z$, supporting the idea that there are
at least two different modes of AGN triggering. In addition, the CLF predicts
that $z\approx 0.9$ quasars may be commonly hosted by haloes with
$M_{\mathrm{h}} \sim 10^{14}$ M$_{\odot}$. These `young cluster' environments
may provide the necessary interactions between gas-rich galaxies to fuel
luminous accretion. The results derived from this method will be useful to
populate AGNs of different luminosities in cosmological simulations. | Cosmological dynamics of multifield dark energy: We numerically and analytically explore the background cosmological dynamics
of multifield dark energy with highly nongeodesic or "spinning" field-space
trajectories. These extensions of standard single-field quintessence possess
appealing theoretical features and observable differences from the cosmological
standard model. At the level of the cosmological background, we perform a
phase-space analysis and identify approximate attractors with late-time
acceleration for a wide range of initial conditions. Focusing on two classes of
field-space geometry, we derive bounds on parameter space by demanding viable
late-time acceleration and the absence of gradient instabilities, as well as
from the de Sitter swampland conjecture. |
The Curious Case of Lyman Alpha Emitters: Growing Younger from z ~ 3 to
z ~ 2?: Lyman Alpha Emitting (LAE) galaxies are thought to be progenitors of
present-day L* galaxies. Clustering analyses have suggested that LAEs at z ~ 3
might evolve into LAEs at z ~ 2, but it is unclear whether the physical nature
of these galaxies is compatible with this hypothesis. Several groups have
investigated the properties of LAEs using spectral energy distribution (SED)
fitting, but direct comparison of their results is complicated by
inconsistencies in the treatment of the data and in the assumptions made in
modeling the stellar populations, which are degenerate with the effects of
galaxy evolution. By using the same data analysis pipeline and SED fitting
software on two stacked samples of LAEs at z = 3.1 and z = 2.1, and by
eliminating several systematic uncertainties that might cause a discrepancy, we
determine that the physical properties of these two samples of galaxies are
dramatically different. LAEs at z = 3.1 are found to be old (age ~ 1 Gyr) and
metal-poor (Z < 0.2 Z_Sun), while LAEs at z = 2.1 appear to be young (age ~ 50
Myr) and metal-rich (Z > Z_Sun). The difference in the observed stellar ages
makes it very unlikely that z = 3.1 LAEs evolve directly into z = 2.1 LAEs.
Larger samples of galaxies, studies of individual objects and spectroscopic
measurements of metallicity at these redshifts are needed to confirm this
picture, which is difficult to reconcile with the effects of 1 Gyr of
cosmological evolution. | Evidence of X-ray emission from the Warm Hot Intergalactic Medium: The Universe has evolved from an initial diffuse, uniform gas to a complex
structure that includes both voids and high-density galaxy clusters connected
by gaseous filaments, known as the Cosmic Web, and traced by 3D surveys of
galaxies. The filamentary structure contains a significant fraction of the
baryonic matter and is predicted to be mostly in the form of a moderately high
temperature plasma, the Warm Hot Intergalactic Medium. Plasma at this
temperature and ionization level emits mostly in soft X-rays. The filamentary
structure, however, is hard to detect because the other sources contributing to
the Diffuse X-ray Background are much brighter and, currently, there are very
few reported detections of emission from the filaments. We report the first
high-confidence level indirect detection of X-ray emission from the Warm Hot
Intergalactic Medium. Applying the Power Spectrum Analysis to XMM-Newton and
eROSITA data, we separated its contribution from other sources modeled in
previous studies. Our result is in good agreement with numerical simulations
and fills a critical gap in the picture of the large-scale structure of the
Universe, in which filamentary gas, galaxies and dark matter interact and
co-evolve. |
Lensed: a code for the forward reconstruction of lenses and sources from
strong lensing observations: Robust modelling of strong lensing systems is fundamental to exploit the
information they contain about the distribution of matter in galaxies and
clusters. In this work, we present Lensed, a new code which performs forward
parametric modelling of strong lenses. Lensed takes advantage of a massively
parallel ray-tracing kernel to perform the necessary calculations on a modern
graphics processing unit (GPU). This makes the precise rendering of the
background lensed sources much faster, and allows the simultaneous optimisation
of tens of parameters for the selected model. With a single run, the code is
able to obtain the full posterior probability distribution for the lens light,
the mass distribution and the background source at the same time. Lensed is
first tested on mock images which reproduce realistic space-based observations
of lensing systems. In this way, we show that it is able to recover unbiased
estimates of the lens parameters, even when the sources do not follow exactly
the assumed model. Then, we apply it to a subsample of the SLACS lenses, in
order to demonstrate its use on real data. The results generally agree with the
literature, and highlight the flexibility and robustness of the algorithm. | Spherical collapse and halo mass function in the symmetron model: We study the gravitational clustering of spherically symmetric overdensities
and the statistics of the resulting dark matter halos in the "symmetron model",
in which a new long range force is mediated by a $Z_2$ symmetric scalar field.
Depending on the initial radius of the overdensity, we identify two distinct
regimes: for small initial radii the symmetron mediated force affects the
spherical collapse at all redshifts; for initial radii larger than some
critical size this force vanishes before collapse because of the symmetron
screening mechanism. In both cases overdensities collapse earlier than in the
$\Lambda$CDM and statistically tend to form more massive dark matter halos.
Regarding the halo-mass function of these objects, we observe order one
departures from standard $\Lambda$CDM predictions. The formalism developed here
can be easily applied to other models where fifth-forces participate to the
dynamics of the gravitational collapse. |
TeV Gamma-Ray Observations of Mrk421 and H1426+428 with TACTIC Imaging
Telescope: We have observed extragalactic sources Mrk421 (z=0.30) and H1426+428
(z=0.129) in very high energy gamma region using TACTIC telescope at Mount Abu,
Rajasthan, India. Mrk421 was observed during 07 December 2005 to 18 April 2007
for a total of ~331hours while H1426+428 was observed for ~244 hours between 22
March 2004 and 11 June 2007. Detailed analysis of Mrk421 data revealed the
presence of a gamma signal with the excess of (~951\pm 82) gamma like events
corresponding to a statistical significance of ~12.0 \sigma in ~97 hours during
27 December 2005 to 07 February 2006. The combined average flux was measured to
be ~(1.04\pm0.14) Crab units. Observed time averaged differential energy
spectrum was found to be consistent with both a pure power law
$d\Phi/dE=(4.66\pm0.46)\times
10^{-11}\,E^{(-3.11\pm0.11)}\,\,cm^{-2}\,s^{-1}\,TeV^{-1}$ and power law with
an exponential cutoff functions $d\Phi/dE=f_0E^{-\Gamma}exp(-E/E_0)$ with
$f_0=(4.88\pm0.38)\times10^{-11}\,cm^{-2}\,s^{-1}\,TeV^{-1}$,
$\Gamma=2.51\pm0.26$ and $E_0=(4.7\pm2.1)TeV$. The later function fits the
observed spectrum well with lower value of reduced $\chi^2$. However, during
the observation period from 18 December 2006 to 18 April 2007, the source was
found to be in a low emission state and we have placed an upper limit of
$1.44\times\,10^{-12}\,photons\,cm^{-2}\,s^{-1}$ at $3\sigma$ level on the
integrated \gam flux above $1\,TeV$. Detailed analysis of H1426+428 data does
not indicate the presence of any statistically significant $TeV$ \gam signal.
Accordingly we have placed an upper limit of
$\leq1.18\times10^{-12}\,photons\,cm^{-2}\,s^{-1}$ on the integrated
$\gamma$-ray flux above $1\,TeV$ at 3$\sigma$ significance level. | Chaplygin gas and the cosmological evolution of alpha: The class of Chaplygin gas models regarded as a candidate of dark energy can
be realized by a scalar field, which could drive the variation of the fine
structure constant $\alpha$ during the cosmic time. This phenomenon has been
observed for almost ten years ago from the quasar absorption spectra and
attracted many attentions. In this paper, we reconstruct the class of Chaplygin
gas models to a kind of scalar fields and confront the resulting
$\Delta\alpha/\alpha$ with the observational constraints. We found that if the
present observational value of the equation of state of the dark energy was not
exactly equal to -1, various parameters of the class of Chaplygin gas models
are allowed to satisfy the observational constraints, as well as the
equivalence principle is also respected. |
Nonparametric reconstruction of the Om diagnostic to test LCDM: Cosmic acceleration is usually related with the unknown dark energy, which
equation of state, w(z), is constrained and numerically confronted with
independent astrophysical data. In order to make a diagnostic of w(z), the
introduction of a null test of dark energy can be done using a diagnostic
function of redshift, Om. In this work we present a nonparametric
reconstruction of this diagnostic using the so-called Loess-Simex factory to
test the concordance model with the advantage that this approach offers an
alternative way to relax the use of priors and find a possible 'w' that
reliably describe the data with no previous knowledge of a cosmological model.
Our results demonstrate that the method applied to the dynamical Om diagnostic
finds a preference for a dark energy model with equation of state w =-2/3,
which correspond to a static domain wall network. | Stochastic gravitational wave background from smoothed cosmic string
loops: We do a complete calculation of the stochastic gravitational wave background
to be expected from cosmic strings. We start from a population of string loops
taken from simulations, smooth these by Lorentzian convolution as a model of
gravitational back reaction, calculate the average spectrum of gravitational
waves emitted by the string population at any given time, and propagate it
through a standard model cosmology to find the stochastic background today. We
take into account all known effects, including changes in the number of
cosmological relativistic degrees of freedom at early times and the possibility
that some energy is in rare bursts that we might never have observed. |
Quartic hilltop inflation revisited: We implement a procedure by which the parameters present in the potential of
Quartic Hilltop Inflation (QHI) are eliminated in favor of the scalar spectral
index $n_s$ and the tensor-to-scalar ratio $r$. By doing this it is posible to
obtain in a straightforward and simple way the equations of a previous analysis
where an analytical treatment of QHI in the large field limit is given. This
procedure also allows a more precise discussion of general properties of the
model. Also, using a constraint from the reheating epoch it is possible to find
bounds for the parameters of the model as well as for quantities of interest
such as the running of the scalar index, the reheating temperature and the
inflationary scale. Since the bounds found come from expressions given
exclusively in terms of $n_s$ and $r$ they will continue to narrow as the
measurements of the observables $n_s$ and $r$ become more sensitive. | DEMNUni: ISW, Rees-Sciama, and weak-lensing in the presence of massive
neutrinos: We present, for the first time in the literature, a full reconstruction of
the total (linear and non-linear) ISW/Rees-Sciama effect in the presence of
massive neutrinos, together with its cross-correlations with CMB-lensing and
weak-lensing signals. The present analyses make use of all-sky maps extracted
via ray-tracing across the gravitational potential distribution provided by the
"Dark Energy and Massive Neutrino Universe" (DEMNUni) project, a set of
large-volume, high-resolution cosmological N-body simulations, where neutrinos
are treated as separate collisionless particles. We correctly recover, at
$1-2\%$ accuracy, the linear predictions from CAMB. Concerning the CMB-lensing
and weak-lensing signals, we also recover, with similar accuracy, the signal
predicted by Boltzmann codes, once non-linear neutrino corrections to Halofit
are accounted for. Interestingly, in the ISW/Rees-Sciama signal, and its cross
correlation with lensing, we find an excess of power with respect to the
massless case, due to free streaming neutrinos, roughly at the transition scale
between the linear and non-linear regimes. The excess is $\sim 5-10\%$ at
$l\sim 100$ for the ISW/Rees-Sciama auto power spectrum, depending on the total
neutrino mass $M_\nu$, and becomes a factor of $\sim 4$ for $M_\nu=0.3$ eV, at
$l\sim 600$, for the ISW/Rees-Sciama cross power with CMB-lensing. This effect
should be taken into account for the correct estimation of the CMB temperature
bispectrum in the presence of massive neutrinos. |
Bispectrum covariance in the flat-sky limit: To probe cosmological fields beyond the Gaussian level, three-point
statistics can be used, all of which are related to the bispectrum. Hence,
measurements of CMB anisotropies, galaxy clustering, and weak gravitational
lensing alike have to rely upon an accurate theoretical background concerning
the bispectrum and its noise properties. If only small portions of the sky are
considered, it is often desirable to perform the analysis in the flat-sky
limit. We aim at a formal, detailed derivation of the bispectrum covariance in
the flat-sky approximation, focusing on a pure two-dimensional Fourier-plane
approach. We define an unbiased estimator of the bispectrum, which takes the
average over the overlap of annuli in Fourier space, and compute its full
covariance. The outcome of our formalism is compared to the flat-sky spherical
harmonic approximation in terms of the covariance, the behavior under parity
transformations, and the information content. We introduce a geometrical
interpretation of the averaging process in the estimator, thus providing an
intuitive understanding. Contrary to foregoing work, we find a difference by a
factor of two between the covariances of the Fourier-plane and the spherical
harmonic approach. We argue that this discrepancy can be explained by the
differing behavior with respect to parity. However, in an exemplary analysis it
is demonstrated that the Fisher information of both formalisms agrees to high
accuracy. Via the geometrical interpretation we are able to link the
normalization in the bispectrum estimator to the area enclosed by the triangle
configuration at consideration as well as to the Wigner symbol, which leads to
convenient approximation formulae for the covariances of both approaches. | Journeying the Redshift Desert: The cosmic star formation rate, AGN activity, galaxy growth, mass assembly
and morphological differentiation all culminate at redshift $\sim 2$. Yet, the
redshift interval $1.4\lsim z\lsim 3$ is harder to explore than the closer and
the more distant Universe. In spite of so much action taking place in this
spacetime portion of the Universe, it has been dubbed the ``Redshift Desert'',
as if very little was happening within its boundaries. The difficulties
encountered in properly mapping the galaxy populations inhabiting the Desert
are illustrated in this paper, along with some possible remedy. |
Star formation in HI tails: HCG 92, HCG 100 and 6 interacting systems: We present new Gemini spectra of 14 new objects found within the HI tails of
Hickson Compact Groups 92 and 100. Nine of them are GALEX Far-UV (FUV) and
Near-UV (NUV) sources. The spectra confirm that these objects are members of
the compact groups and have metallicities close to solar, with an average value
of 12+log(O/H)~8.5. They have average FUV luminosities 7 x 10^40 erg/s, very
young ages (< 100 Myr) and two of them resemble tidal dwarf galaxies (TDGs)
candidates. We suggest that they were created within gas clouds that were
ejected during galaxy-galaxy interactions into the intergalactic medium, which
would explain the high metallicities of the objects, inherited from the parent
galaxies from which the gas originated. We conduct a search for similar objects
in 6 interacting systems with extended HI tails, NGC 2623, NGC 3079, NGC 3359,
NGC 3627, NGC 3718, NGC 4656. We found 35 UV sources with ages < 100 Myr,
however most of them are on average less luminous/massive than the UV sources
found around HCG 92 and 100. We speculate that this might be an environmental
effect and that compact groups of galaxies are more favorable to TDG formation
than other interacting systems. | Wiggly Whipped Inflation: Motivated by BICEP2 results on the CMB polarization B-mode which imply
primordial gravitational waves are produced when the Universe has the expansion
rate of about $H \approx 10^{14}$ GeV, and by deviations from a smooth
power-law behaviour for multipoles $\ell <50$ in the CMB temperature anisotropy
power spectrum found in the WMAP and Planck experiments, we have expanded our
class of large field inflationary models that fit both the BICEP2 and Planck
CMB observations consistently. These best-fitted large field models are found
to have a transition from a faster roll to the slow roll $V(\phi)=m^2 \phi^2/2$
inflation at a field value around 14.6~${\rm M_{Pl}}$ and thus a potential
energy of $V(\phi) \sim (10^{16}\,{\rm GeV})^4$. In general this transition
with sharp features in the inflaton potential produces not only suppression of
scalars relative to tensor modes at small $k$ but also introduces wiggles in
the primordial perturbation spectrum. These wiggles are shown to be useful to
explain some localized features in the CMB angular power spectrum and can also
have other observational consequences. Thus, primordial GW can be used now to
make a tomography of inflation determining its fine structure. The resulting
Wiggly Whipped Inflation scenario is described in details and the anticipated
perturbation power spectra, CMB power spectra, non-Gaussianity and other
observational consequences are calculated and compared to existing and
forthcoming observations. |
Dark energy, scalar singlet dark matter and the Higgs portal: One of the simplest extensions of the Standard Model (SM) comprises the
inclusion of a massive real scalar field, neutral under the SM gauge groups, to
be a dark matter candidate. The addition of a dimension-six term into the
potential of the scalar dark matter enables the appearance of a false vacuum
that describes the cosmic acceleration. We show that the running of the singlet
self-interaction and the Higgs portal coupling differs from the standard scalar
singlet dark matter model. If we maintain a positive quartic coupling, it is
also possible to describe the accelerated expansion of the Universe through a
false vacuum with the addition of a dimension-eight interaction term. In this
case, where the potential remains bounded from below at low energies, the false
vacuum decay is highly suppressed. | Evidence for Scale Factor Oscillations Observed in the Large Scale
Structure of the Universe: We present two independent analyses as further evidence that galaxy
clustering at scales of 500 Mpc and greater has a periodic time component
induced by oscillations in the scale factor at a frequency of approximately 7
cycles over one Hubble time. The scale factor oscillations were discovered in
previous work by analyzing the Hubble diagram for type 1a SNe data. In the
present work we analyze galaxy number count data from SDSSIII-BOSS, DR9 using a
simple oscillating expanding space model and also perform a Fourier analysis of
the same SDSSIII data set . The number distribution of galaxies on these scales
should be relatively smooth. However, a DR9 plot of galaxy number count per
0.01 redshift bin as a function of redshift shows significant bumps to redshift
0.5. Later releases show the same behavior. Our model fits essentially all
bumps at 99.8% confidence once the oscillation is included. A Fourier analysis
of the same number count vs. redshift data (processed only to convert redshift
to equal time bins) clearly shows the dominant 7-cycle signal at 15/1
signal-to-noise ratio. The DR9 galaxy number count peaks near redshift 0.5 and
then falls off due to target magnitude limitations. In our model we assume
ideal observation to all redshifts. The oscillation model displays a matching
peak at redshift 0.5, then falls, but continues on to rise predicting a second
peak at redshift 0.64. Confirmation of the second peak from future SDSSIV data
to higher redshift would further support our observation of oscillations in the
scale factor. The oscillations may derive from a scalar field model of dark
matter as shown in our earlier work. |
Search for solar axions in XMASS, a large liquid-xenon detector: XMASS, a low-background, large liquid-xenon detector, was used to search for
solar axions that would be produced by bremsstrahlung and Compton effects in
the Sun. With an exposure of 5.6ton days of liquid xenon, the model-independent
limit on the coupling for mass $\ll$ 1keV is $|g_{aee}|< 5.4\times 10^{-11}$
(90% C.L.), which is a factor of two stronger than the existing experimental
limit. The bounds on the axion masses for the DFSZ and KSVZ axion models are
1.9 and 250eV, respectively. In the mass range of 10-40keV, this study produced
the most stringent limit, which is better than that previously derived from
astrophysical arguments regarding the Sun to date. | Galaxy clustering and projected density profiles as traced by satellites
in photometric surveys: Methodology and luminosity dependence: We develop a new method which measures the projected density distribution
w_p(r_p)n of photometric galaxies surrounding a set of
spectroscopically-identified galaxies, and simultaneously the projected
correlation function w_p(r_p) between the two populations. In this method we
are able to divide the photometric galaxies into subsamples in luminosity
intervals when redshift information is unavailable, enabling us to measure
w_p(r_p)n and w_p(r_p) as a function of not only the luminosity of the
spectroscopic galaxy, but also that of the photometric galaxy. Extensive tests
show that our method can measure w_p(r_p) in a statistically unbiased way. The
accuracy of the measurement depends on the validity of the assumption in the
method that the foreground/background galaxies are randomly distributed and
thus uncorrelated with those galaxies of interest. Therefore, our method can be
applied to the cases where foreground/background galaxies are distributed in
large volumes, which is usually valid in real observations. We applied our
method to data from SDSS including a sample of 10^5 LRGs at z~0.4 and a sample
of about half a million galaxies at z~0.1, both of which are cross-correlated
with a deep photometric sample drawn from the SDSS. On large scales, the
relative bias factor of galaxies measured from w_p(r_p) at z~0.4 depends on
luminosity in a manner similar to what is found at z~0.1, which are usually
probed by autocorrelations of spectroscopic samples. On scales smaller than a
few Mpc and at both z~0.4 and z~0.1, the photometric galaxies of different
luminosities exhibit similar density profiles around spectroscopic galaxies at
fixed luminosity and redshift. This provides clear support for the assumption
commonly-adopted in HOD models that satellite galaxies of different
luminosities are distributed in a similar way, following the dark matter
distribution within their host halos. |
Cross-correlation of gravitational lensing from DES Science Verification
data with SPT and Planck lensing: We measure the cross-correlation between weak lensing of galaxy images and of
the cosmic microwave background (CMB). The effects of gravitational lensing on
different sources will be correlated if the lensing is caused by the same mass
fluctuations. We use galaxy shape measurements from 139 deg$^{2}$ of the Dark
Energy Survey (DES) Science Verification data and overlapping CMB lensing from
the South Pole Telescope (SPT) and Planck. The DES source galaxies have a
median redshift of $z_{\rm med} {\sim} 0.7$, while the CMB lensing kernel is
broad and peaks at $z{\sim}2$. The resulting cross-correlation is maximally
sensitive to mass fluctuations at $z{\sim}0.44$. Assuming the Planck 2015
best-fit cosmology, the amplitude of the DES$\times$SPT cross-power is found to
be $A = 0.88 \pm 0.30$ and that from DES$\times$Planck to be $A = 0.86 \pm
0.39$, where $A=1$ corresponds to the theoretical prediction. These are
consistent with the expected signal and correspond to significances of $2.9
\sigma$ and $2.2 \sigma$ respectively. We demonstrate that our results are
robust to a number of important systematic effects including the shear
measurement method, estimator choice, photometric redshift uncertainty and CMB
lensing systematics. Significant intrinsic alignment of galaxy shapes would
increase the cross-correlation signal inferred from the data; we calculate a
value of $A = 1.08 \pm 0.36$ for DES$\times$SPT when we correct the
observations with a simple IA model. With three measurements of this
cross-correlation now existing in the literature, there is not yet reliable
evidence for any deviation from the expected LCDM level of cross-correlation,
given the size of the statistical uncertainties and the significant impact of
systematic errors, particularly IAs. We provide forecasts for the expected
signal-to-noise of the combination of the five-year DES survey and SPT-3G. | NGC 2782: a merger remnant with young stars in its gaseous tidal tail: We have searched for young star-forming regions around the merger remnant NGC
2782. By using GALEX FUV and NUV imaging and HI data we found seven UV sources,
located at distances greater than 26 kpc from the center of NGC 2782, and
coinciding with its western HI tidal tail. These regions were resolved in
several smaller systems when Gemini/GMOS r-band images were used. We compared
the observed colors to stellar population synthesis models and we found that
these objects have ages of ~1 to 11 Myr and masses ranging from 10^3.9 to
10^4.6 Msun. By using Gemini/GMOS spectroscopic data we confirm memberships and
derive high metallicities for three of the young regions in the tail
(12+log(O/H)=8.74\pm0.20, 8.81\pm0.20 and 8.78\pm0.20). These metallicities are
similar to the value presented by the nuclear region of NGC 2782 and also
similar to the value presented for an object located close to the main body of
NGC 2782. The high metallicities measured for the star-forming regions in the
gaseous tidal tail of NGC 2782 could be explained if they were formed out of
highly enriched gas which was once expelled from the center of the merging
galaxies when the system collided. An additional possibility is that the tail
has been a nursery of a few generations of young stellar systems which
ultimately polluted this medium with metals, further enriching the already
pre-enriched gas ejected to the tail when the galaxies collided. |
Measures of Galaxy Environment - I. What is "Environment"?: The influence of a galaxy's environment on its evolution has been studied and
compared extensively in the literature, although differing techniques are often
used to define environment. Most methods fall into two broad groups: those that
use nearest neighbours to probe the underlying density field and those that use
fixed apertures. The differences between the two inhibit a clean comparison
between analyses and leave open the possibility that, even with the same data,
different properties are actually being measured. In this work we apply twenty
published environment definitions to a common mock galaxy catalogue constrained
to look like the local Universe. We find that nearest neighbour-based measures
best probe the internal densities of high-mass haloes, while at low masses the
inter-halo separation dominates and acts to smooth out local density
variations. The resulting correlation also shows that nearest neighbour galaxy
environment is largely independent of dark matter halo mass. Conversely,
aperture-based methods that probe super-halo scales accurately identify
high-density regions corresponding to high mass haloes. Both methods show how
galaxies in dense environments tend to be redder, with the exception of the
largest apertures, but these are the strongest at recovering the background
dark matter environment. We also warn against using photometric redshifts to
define environment in all but the densest regions. When considering environment
there are two regimes: the 'local environment' internal to a halo best measured
with nearest neighbour and 'large-scale environment' external to a halo best
measured with apertures. This leads to the conclusion that there is no
universal environment measure and the most suitable method depends on the scale
being probed. | Extending the supernova Hubble diagram to z~1.5 with the Euclid space
mission: We forecast dark energy constraints that could be obtained from a new large
sample of Type Ia supernovae where those at high redshift are acquired with the
Euclid space mission. We simulate a three-prong SN survey: a z<0.35 nearby
sample (8000 SNe), a 0.2<z<0.95 intermediate sample (8800 SNe), and a
0.75<z<1.55 high-z sample (1700 SNe). The nearby and intermediate surveys are
assumed to be conducted from the ground, while the high-z is a joint ground-
and space-based survey. This latter survey, the "Dark Energy Supernova
Infra-Red Experiment" (DESIRE), is designed to fit within 6 months of Euclid
observing time, with a dedicated observing program. We simulate the SN events
as they would be observed in rolling-search mode by the various instruments,
and derive the quality of expected cosmological constraints. We account for
known systematic uncertainties, in particular calibration uncertainties
including their contribution through the training of the supernova model used
to fit the supernovae light curves. Using conservative assumptions and a 1-D
geometric Planck prior, we find that the ensemble of surveys would yield
competitive constraints: a constant equation of state parameter can be
constrained to sigma(w)=0.022, and a Dark Energy Task Force figure of merit of
203 is found for a two-parameter equation of state. Our simulations thus
indicate that Euclid can bring a significant contribution to a purely
geometrical cosmology constraint by extending a high-quality SN Hubble diagram
to z~1.5. We also present other science topics enabled by the DESIRE Euclid
observations |
A high-resolution self-consistent whole sky foreground model: The neutral hydrogen 21cm line is potentially a very powerful probe of the
observable universe, and a number of on-going experiments are trying to detect
it at cosmological distances. However, the presence of strong foreground
radiations such as the galactic synchrotron radiation, galactic free-free
emission and extragalactic radio sources make it a very challenging task. For
the design of 21cm experiments and analysis of their data, simulation is an
essential tool, and good sky foreground model is needed. With existing data the
whole sky maps are available only in low angular resolutions or for limited
patches of sky, which is inadequate in the simulation of these new 21cm
experiments. In this paper, we present the method of constructing a high
resolution self-consistent sky model at low frequencies, which incorporates
both diffuse foreground and point sources. Our diffuse map is constructed by
generating physical foreground components including the galactic synchrotron
emission and galactic free-free emission. The point source sample is generated
using the actual data from the NRAO VLA Sky Survey (NVSS) and the Sydney
University Molonglo Sky Survey (SUMSS) where they are available and complete in
flux limit, and mock point sources according to statistical distributions. The
entire model is made self-consistent by removing the integrated flux of the
point sources from the diffuse map so that this part of radiation is not double
counted. We show that with the point sources added, a significant angular power
is introduced in the mock sky map, which may be important for foreground
subtraction simulations. Our sky maps and point source catalogues are available
to download. | Constraints on primordial non-Gaussianity from Galaxy-CMB lensing
cross-correlation: Recent studies have shown that the primordial non-Gaussianity affects
clustering of dark matter halos through a scale-dependent bias and various
constraints on the non-Gaussianity through this scale-dependent bias have been
placed. Here we introduce the cross-correlation between the CMB lensing
potential and the galaxy angular distribution to effectively extract
information about the bias from the galaxy distribution. Then, we estimate the
error of non-linear parameter, f_NL, for the on-going CMB experiments and
galaxy surveys, such as Planck and Hyper Suprime-Cam (HSC). We found that for
the constraint on f_NL with Planck and HSC, the wide field galaxy survey is
preferable to the deep one, and the expected error on f_NL can be as small as:
\Delta f_NL ~ 20 for b_0 = 2 and \Delta f_NL ~ 10 for b_0 = 4, where b_0 is the
linear bias parameter. It is also found that future wide field galaxy survey
could achieve \Delta f_NL ~ 5 with CMB prior from Planck if one could observe
highly biased objects at higher redshift (z ~ 2). |
Dependence of direct detection signals on the WIMP velocity distribution: The signals expected in WIMP direct detection experiments depend on the
ultra-local dark matter distribution. Observations probe the local density,
circular speed and escape speed, while simulations find velocity distributions
that deviate significantly from the standard Maxwellian distribution. We
calculate the energy, time and direction dependence of the event rate for a
range of velocity distributions motivated by recent observations and
simulations, and also investigate the uncertainty in the determination of WIMP
parameters. The dominant uncertainties are the systematic error in the local
circular speed and whether or not the MW has a high density dark disc. In both
cases there are substantial changes in the mean differential event rate and the
annual modulation signal, and hence exclusion limits and determinations of the
WIMP mass. The uncertainty in the shape of the halo velocity distribution is
less important, however it leads to a 5% systematic error in the WIMP mass. The
detailed direction dependence of the event rate is sensitive to the velocity
distribution. However the numbers of events required to detect anisotropy and
confirm the median recoil direction do not change substantially. | On the formation time scale of massive cluster ellipticals based on deep
near-IR spectroscopy at z~2: We present improved constraints on the formation time scale of massive
cluster galaxies based on rest-frame optical spectra of galaxies in a forming
cluster located at z=2.16. The spectra are obtained with MOIRCS on the Subaru
telescope with an integration time of ~7 hours. We achieve accurate redshift
measurements by fitting SEDs using the spectra and broad-band photometry
simultaneously, allowing us to identify probable cluster members. Clusters at
low redshifts are dominated by quiescent galaxies, but we find that quiescent
galaxies and star forming galaxies co-exist in this z=2 system. Interestingly,
the quiescent galaxies form a weak red sequence in the process of forming. By
stacking the spectra of star forming galaxies, we observe strong emission lines
such as [OII] and [OIII] and we obtain a tentative hint of AGN activities in
these galaxies. On the other hand, the stacked spectrum of the quiescent
galaxies reveals a clear 4000A break with a possible CaII H+K absorption
feature and strong emission lines such as [OII] are absent in the spectrum,
confirming the quiescent nature of these galaxies. We then perform detailed
spectral analyses of the stacked spectrum, which suggest that these massive
quiescent galaxies formed at redshifts between 3 and 4 on a time scale of <~0.5
Gyr. This short formation time scale is not reproduced in recent numerical
simulations. We discuss possible mechanisms for how these galaxies form 10^11
Msun stellar mass on a short time scale and become red and quiescent by z=2. |
Density fields and halo mass functions in the Geometrical Adhesion toy
Model: In dimension 2 and above, the Burgers dynamics, the so-called "adhesion
model" in cosmology, can actually give rise to several dynamics in the inviscid
limit. We investigate here the statistical properties of the density field when
it is defined by a "geometrical model" associated with this Burgers velocity
field and where the matter distribution is fully determined, at each time step,
by geometrical constructions. Our investigations are based on a set of
numerical experiments that make use of an improved algorithm, for which the
geometrical constructions are efficient and robust. In this work we focus on
Gaussian initial conditions with power-law power spectra of slope $n$ in the
range $-3<n<1$, where a self-similar evolution develops, and we compute the
behavior of power spectra, density probability distributions and mass
functions. As expected for such dynamics, the density power spectra show
universal high-$k$ tails that are governed by the formation of pointlike
masses. The two other statistical indicators however show the same qualitative
properties as those observed for 3D gravitational clustering. In particular,
the mass functions obey a Press-Schechter like scaling up to a very good
accuracy in 1D, and to a lesser extent in 2D. Our results suggest that the
"geometrical adhesion model", whose solution is fully known at all times,
provides a precious tool to understand some of the statistical constructions
frequently used to study the development of mass halos in gravitational
clustering. | High-resolution observations of two OVI absorbers at z=2 towards PKS
1448-232: To explore the ionization conditions in highly-ionized absorbers at high
redshift we have studied in detail two intervening OVI absorbers at z=2 towards
the quasar PKS1448-232, based on high (R=75,000) and intermediate (R=45,000)
resolution optical VLT/UVES spectra. We find that both absorption systems are
composed of several narrow subcomponents with CIV/OVI Doppler-parameters b<10
km/s, typically. This implies that the gas temperatures are T<10^5 K and that
the absorbers are photoionized by the UV background. The system at z=2.1098
represents a simple, isolated OVI absorber that has only two absorption
components and that is relatively metal-rich (Z\sim 0.6 solar). Ioinization
modeling implies that the system is photoionized with OVI, CIV, and HI
coexisting in the same gas phase. The second system at z=2.1660 represents a
complicated, multi-component absorption system with eight OVI components
spanning almost 300 km/s in radial velocity. The photoionization modeling
implies that the metallicity is non-uniform and relatively low (<= 0.1 solar)
and that the OVI absorption must arise in a gas phase different from that
traced by CIV, CIII, and HI. Our detailed study of the two OVI systems towards
PKS1448-232 shows that multi-phase, multi-component high-ion absorbers like the
one at z=2.1660 require a detailed ionization modeling of the various
subcomponents to obtain reliable results on the physical conditions and
metal-abundances in the gas. |
Modelling non-dust fluids in cosmology: Currently, most of the numerical simulations of structure formation use
Newtonian gravity. When modelling pressureless dark matter, or `dust', this
approach gives the correct results for scales much smaller than the
cosmological horizon, but for scenarios in which the fluid has pressure this is
no longer the case. In this article, we present the correspondence of
perturbations in Newtonian and cosmological perturbation theory, showing exact
mathematical equivalence for pressureless matter, and giving the relativistic
corrections for matter with pressure. As an example, we study the case of
scalar field dark matter which features non-zero pressure perturbations. We
discuss some problems which may arise when evolving the perturbations in this
model with Newtonian numerical simulations and with CMB Boltzmann codes. | Predicting the CIB-$φ$ contamination in the cross-correlation of the
tSZ effect and $φ$: The recent release of {\it Planck} data gives access to a full sky coverage
of the thermal Sunyaev-Zel'dovich (tSZ) effect and of the cosmic microwave
background (CMB) lensing potential ($\phi$).
The cross-correlation of these two probes of the large-scale structures in
the Universe is a powerful tool for testing cosmological models, especially in
the context of the difference between galaxy clusters and CMB for the
best-fitting cosmological parameters.
However, the tSZ effect maps are highly contaminated by cosmic infra-red
background (CIB) fluctuations.
Unlike other astrophysical components, the spatial distribution of CIB varies
with frequency.
Thus it cannot be completely removed from a tSZ Compton parameter map, which
is constructed from a linear combination of multiple frequency maps.
We have estimated the contamination of the CIB-$\phi$ correlation in the
tSZ-$\phi$ power-spectrum.
We considered linear combinations that reconstruct the tSZ Compton parameter
from {\it Planck} frequency maps.
We conclude that even in an optimistic case, the CIB-$\phi$ contamination is
significant with respect to the tSZ-$\phi$ signal itself.
Consequently, We stress that tSZ-$\phi$ analyses that are based on Compton
parameter maps are highly limited by the bias produced by CIB-$\phi$
contamination. |
Dark Energy Survey Year 3 Results: Exploiting small-scale information
with lensing shear ratios: Using the first three years of data from the Dark Energy Survey, we use
ratios of small-scale galaxy-galaxy lensing measurements around the same lens
sample to constrain source redshift uncertainties, intrinsic alignments and
other nuisance parameters of our model. Instead of using a simple geometric
approach for the ratios, we use the full modeling of the galaxy-galaxy lensing
measurements, including the corresponding integration over the power spectrum
and the contributions from intrinsic alignments and lens magnification. We
perform extensive testing of the small-scale shear ratio (SR) modeling by
studying the impact of different effects such as the inclusion of baryonic
physics, non-linear biasing, halo occupation distribution descriptions and lens
magnification, among others, and using realistic $N$-body simulations. We
validate the robustness of our constraints in the data by using two independent
lens samples, and by deriving constraints using the corresponding large-scale
ratios for which the modeling is simpler. The DES Y3 results demonstrate how
the ratios provide significant improvements in constraining power for several
nuisance parameters in our model, especially on source redshift calibration and
intrinsic alignments (IA). For source redshifts, SR improves the constraints
from the prior by up to 38\% in some redshift bins. Such improvements, and
especially the constraints it provides on IA, translate to tighter cosmological
constraints when SR is combined with cosmic shear and other 2pt functions. In
particular, for the DES Y3 data, SR improves $S_8$ constraints from cosmic
shear by up to 31\%, and for the full combination of probes (3$\times$2pt) by
up to 10\%. The shear ratios presented in this work are used as an additional
likelihood for cosmic shear, 2$\times$2pt and the full 3$\times$2pt in the
fiducial DES Y3 cosmological analysis. | Non-perturbative non-Gaussianity and primordial black holes: We present a non-perturbative method for calculating the abundance of
primordial black holes given an arbitrary one-point probability distribution
function for the primordial curvature perturbation, $P(\zeta)$. A
non-perturbative method is essential when considering non-Gaussianities that
cannot be treated using a conventional perturbative expansion. To determine the
full statistics of the density field, we relate $\zeta$ to a Gaussian field by
equating the cumulative distribution functions. We consider two examples: a
specific local-type non-Gaussian distribution arising from ultra slow roll
models, and a general piecewise model for $P(\zeta)$ with an exponential tail.
We demonstrate that the enhancement of primordial black hole formation is due
to the intermediate regime, rather than the far tail. We also show that
non-Gaussianity can have a significant impact on the shape of the primordial
black hole mass distribution. |
Sampling the Probability Distribution of Type Ia Supernova Lightcurve
Parameters in Cosmological Analysis: In order to obtain robust cosmological constraints from Type Ia supernova (SN
Ia) data, we have applied Markov Chain Monte Carlo (MCMC) to SN Ia lightcurve
fitting. We develop a method for sampling the resultant probability density
distributions (pdf) of the SN Ia lightcuve parameters in the MCMC likelihood
analysis to constrain cosmological parameters, and validate it using simulated
data sets. Applying this method to the Joint Lightcurve Analysis (JLA) data set
of SNe Ia, we find that sampling the SN Ia lightcurve parameter pdf's leads to
cosmological parameters closer to that of a flat Universe with a cosmological
constant, compared to the usual practice of using only the best fit values of
the SN Ia lightcurve parameters. Our method will be useful in the use of SN Ia
data for precision cosmology. | Rest-frame ultra-violet spectra of massive galaxies at z=3: evidence of
high-velocity outflows: Galaxy formation models invoke the presence of strong feedback mechanisms
that regulate the growth of massive galaxies at high redshifts. In this paper
we aim to: (1) confirm spectroscopically the redshifts of a sample of massive
galaxies selected with photometric redshifts z > 2.5; (2) investigate the
properties of their stellar and interstellar media; (3) detect the presence of
outflows, and measure their velocities. To achieve this, we analysed deep,
high-resolution (R~2000) FORS2 rest-frame UV spectra for 11 targets. We
confirmed that 9 out of 11 have spectroscopic redshifts z > 2.5. We also
serendipitously found two mask fillers at redshift z > 2.5, which originally
were assigned photometric redshifts 2.0 < z < 2.5. In the four highest-quality
spectra we derived outflow velocities by fitting the absorption line profiles
with models including multiple dynamical components. We found strongly
asymmetric, high-ionisation lines, from which we derived outflow velocities
ranging from 480 to 1518 km/s. The two galaxies with highest velocity show
signs of AGN. We revised the spectral energy distribution fitting U-band
through 8 micron photometry, including the analysis of a power-law component
subtraction to identify the possible presence of active galactic nuclei (AGN).
The revised stellar masses of all but one of our targets are >1e10 Msun, with
four having stellar masses > 5e10 Msun. Three galaxies have a significant
power-law component in their spectral energy distributions, which indicates
that they host AGN. We conclude that massive galaxies are characterised by
significantly higher velocity outflows than the typical Lyman break galaxies at
z ~ 3. The incidence of high-velocity outflows (~40% within our sample) is also
much higher than among massive galaxies at z < 1, which is consistent with the
powerful star formation and nuclear activity that most massive galaxies display
at z > 2. |
A comparative analysis of virial black-hole mass estimates of
moderate-luminosity active galactic nuclei using Subaru/FMOS: We present an analysis of broad emission lines observed in
moderate-luminosity active galactic nuclei (AGNs), typical of those found in
X-ray surveys of deep fields, with the aim to test the validity of single-epoch
virial black hole mass estimates. We have acquired near-infrared (NIR) spectra
of AGNs up to z ~ 1.8 in the COSMOS and Extended Chandra Deep Field-South
Survey, with the Fiber Multi-Object Spectrograph (FMOS) mounted on the Subaru
Telescope. These low-resolution NIR spectra provide a significant detection of
the broad Halpha line that has been shown to be a reliable probe of black hole
mass at low redshift. Our sample has existing optical spectroscopy which
provides a detection of MgII, a broad emission line typically used for black
hole mass estimation at z > 1. We carry out a spectral-line fitting procedure
using both Halpha and MgII to determine the virial velocity of gas in the broad
line region, the monochromatic continuum luminosity at 3000 A, and the total
Halpha line luminosity. With a sample of 43 AGNs spanning a range of two
decades in luminosity (i.e., L ~ 10^44-46 ergs/s), we find a tight correlation
between the continuum and line luminosity with a distribution characterized by
<log(L_3000/L_Halpha)> = 1.52 and a dispersion sigma = 0.16. There is also a
close one-to-one relationship between the FWHM of Halpha and of MgII up to
10000 km/s with a dispersion of 0.14 in the distribution of the logarithm of
their ratios. Both of these then lead to there being very good agreement
between Halpha- and MgII-based masses over a wide range in black hole mass
(i.e., M_BH ~ 10^7-9 M_sun). We do find a small offset in MgII-based masses,
relative to those based on Halpha, of +0.17 dex and a dispersion sigma = 0.32.
In general, these results demonstrate that local scaling relations, using MgII
or Halpha, are applicable for AGN at moderate luminosities and up to z ~ 2. | Probing the cross-power of unresolved cosmic infrared and X-ray
backgrounds with upcoming space missions: The source-subtracted cosmic infrared background (CIB) fluctuations uncovered
in deep Spitzer data cannot be explained by known galaxy populations and appear
strongly coherent with unresolved cosmic X-ray background (CXB). This suggests
that the source-subtracted CIB contains emissions from significantly abundant
accreting black holes (BHs). We show that theoretically such populations would
have the angular power spectrum which is largely independent of the epochs
occupied by these sources, provided they are at z>~ 4, offering an important
test of the origin of the new populations. Using the current measurements we
reconstruct the underlying soft X-ray CXB from the new sources and show that
its fluctuations, while consistent with a high-z origin, have an amplitude that
cannot be reached in direct measurements with the foreseeable X-ray space
missions. This necessitates application of the methods developed by the authors
to future IR and X-ray datasets, which must cover large areas of the sky in
order to measure the signal with high precision. The LIBRAE project within
ESA's Euclid mission will probe source-subtracted CIB over ~1/2 the sky at
three near-IR bands, and its cross-power with unresolved CXB can be measured
then from the concurrent eROSITA mission covering the same areas of the sky. We
discuss the required methodology for this measurement and evaluate its
projected S/N to show the unique potential of this experimental configuration
to accurately probe the CXB from the new BH sources and help identify their
epochs. |
Ultracompact minihalos associated with stellar-mass primordial black
holes: The possibility that primordial black hole binary mergers of stellar mass can
explain the signals detected by the gravitational-wave interferometers has
attracted much attention. In this scenario, primordial black holes can comprise
only part of the entire dark matter, say, of order 0.1 %. This implies that
most of the dark matter is accounted for by a different component, such as
Weakly Interacting Massive Particles. We point out that in this situation, very
compact dark matter minihalos, composed of the dominant component of the dark
matter, are likely to be formed abundantly in the early Universe, with their
formation redshift and abundance depending on primordial non-Gaussianity. They
may be detected in future experiments via pulsar observations. | The Black Hole and Central Stellar Population of MCG--6-30-15: We present the first near-infrared integral field spectroscopy observations
of the galaxy MCG--6-30-15. The H-band data studied in this paper cover the
central 500 pc of the galaxy at the best resolution (0".1) so far. The spectra
of the innermost regions are dominated by broad brackett series emission lines
and non-stellar continuum, under which we are able to trace the distribution
and kinematics of the stars and also the [Fe II] line emission. We find that
there is a counter-rotating stellar core extending out to 125 pc, which appears
to be associated with the [Fe II] emission. Based on the mass-to-light ratio,
and the presence of this emission line, we estimate the age of the central
stellar population to be of order of 65 Myr. We show that the gas needed to
fuel the black hole is, at most, only 1 per cent of that needed to form these
stars. We derive independent constraints on the black hole mass using the
dynamical information and determine an upper limit for the black hole mass, Mbh
< 6e7 Msun, that is consistent with other estimates. |
Light Sterile Neutrinos and Inflationary Freedom: We perform a cosmological analysis in which we allow the primordial power
spectrum of scalar perturbations to assume a shape that is different from the
usual power-law predicted by the simplest models of cosmological inflation. We
parameterize the free primordial power spectrum with a "piecewise cubic Hermite
interpolating polynomial" (PCHIP). We consider a 3+1 neutrino mixing model with
a sterile neutrino having a mass at the eV scale, which can explain the
anomalies observed in short-baseline neutrino oscillation experiments. We find
that the freedom of the primordial power spectrum allows to reconcile the
cosmological data with a fully thermalized sterile neutrino in the early
Universe. Moreover, the cosmological analysis gives us some information on the
shape of the primordial power spectrum, which presents a feature around the
wavenumber $k=0.002\,\text{Mpc}^{-1}$. | Cosmology-independent Estimate of the Hubble Constant and Spatial
Curvature Using Time-delay Lenses and Quasars: With the distance sum rule in the Friedmann-Lema\^{\i}tre-Robertson-Walker
metric, model-independent constraints on both the Hubble constant $H_0$ and
spatial curvature $\Omega_{K}$ can be obtained using strong lensing time-delay
data and Type Ia supernova (SN Ia) luminosity distances. This method is limited
by the relative low redshifts of SNe Ia, however. Here, we propose using
quasars as distance indicators, extending the coverage to encompass the
redshift range of strong lensing systems. We provide a novel and improved
method of determining $H_0$ and $\Omega_{K}$ simultaneously. By applying this
technique to the time-delay measurements of seven strong lensing systems and
the known ultraviolet versus X-ray luminosity correlation of quasars, we
constrain the possible values of both $H_0$ and $\Omega_{K}$, and find that
$H_0=75.3^{+3.0}_{-2.9}$ km $\rm s^{-1}$ $\rm Mpc^{-1}$ and
$\Omega_{K}=-0.01^{+0.18}_{-0.17}$. The measured $\Omega_{K}$ is consistent
with zero spatial curvature, indicating that there is no significant deviation
from a flat universe. If we use flatness as a prior, we infer that
$H_0=75.3^{+1.9}_{-1.9}$ km $\rm s^{-1}$ $\rm Mpc^{-1}$, representing a
precision of 2.5\%. If we further combine these data with the 1048 current
Pantheon SNe Ia, our model-independent constraints can be further improved to
$H_0=75.3^{+3.0}_{-2.9}$ km $\rm s^{-1}$ $\rm Mpc^{-1}$ and
$\Omega_{K}=0.05^{+0.16}_{-0.14}$. In every case, we find that the Hubble
constant measured with this technique is strongly consistent with the value
($\sim 74$ km $\rm s^{-1}$ $\rm Mpc^{-1}$) measured using the local distance
ladder, as opposed to the value optimized by {\it Planck}. |
DM haloes in the fifth-force cosmology: We investigate how long-range scalar interactions affect the properties of
dark matter haloes. For doing so we employ the ReBEL model which implements an
additional interaction between dark matter particles. On the phenomenological
level this is equivalent to a modification of gravity. We analyse the
differences between five ReBEL models and $\Lambda$CDM using a series of high
resolution cosmological simulations. Emphasis is placed on investigating how
halo properties change in the presence of a fifth force. We report that the
density profile of ReBEL haloes is well described by the NFW profile but with
mean concentrations from $5\%$ to a few times higher than the standard
$\Lambda$CDM value. We also find a slight increase of the halo spin for haloes
more massive than $5\times10^{11}\M_{\odot}$, reflecting a higher rotational
support of those haloes due to scalar forces. In addition, the dark matter
haloes in our models are more spherical than their counterparts in
$\Lambda$CDM. The ReBEL haloes are also more virialised, with a large
difference from $\Lambda$CDM for strong fifth forces and a much smaller change
for weak scalar interactions. | The Bologna complete sample of nearby radio sources: II -- phase
referenced observations of faint nuclear sources: To study statistical properties of different classes of sources, it is
necessary to observe a sample that is free of selection effects. To do this, we
initiated a project to observe a complete sample of radio galaxies selected
from the B2 Catalogue of Radio Sources and the Third Cambridge Revised
Catalogue (3CR), with no selection constraint on the nuclear properties. We
named this sample "the Bologna Complete Sample" (BCS). We present new VLBI
observations at 5 and 1.6 GHz for 33 sources drawn from a sample not biased
toward orientation. By combining these data with those in the literature,
information on the parsec-scale morphology is available for a total of 76 of 94
radio sources with a range in radio power and kiloparsec-scale morphologies.
The fraction of two-sided sources at milliarcsecond resolution is high (30%),
compared to the fraction found in VLBI surveys selected at centimeter
wavelengths, as expected from the predictions of unified models. The
parsec-scale jets are generally found to be straight and to line up with the
kiloparsec-scale jets. A few peculiar sources are discussed in detail. |
Supersymmetric Dark Matter Candidates: After reviewing the theoretical, phenomenological and experimental
motivations for supersymmetric extensions of the Standard Model, we recall that
supersymmetric relics from the Big Bang are expected in models that conserve R
parity. We then discuss possible supersymmetric dark matter candidates,
focusing on the lightest neutralino and the gravitino. In the latter case, the
next-to-lightest supersymmetric particle is expected to be long-lived, and
possible candidates include spartners of the tau lepton, top quark and
neutrino. We then discuss the roles of the renormalization-group equations and
electroweak symmetry breaking in delimiting the supersymmetric parameter space.
We discuss in particular the constrained minimal extension of the Standard
Model (CMSSM), in which the supersymmetry-breaking parameters are assumed to be
universal at the grand unification scale, presenting predictions from a
frequentist analysis of its parameter space. We also discuss astrophysical and
cosmological constraints on gravitino dark matter models, as well as the
parameter space of minimal supergravity (mSUGRA) models in which there are
extra relations between the trilinear and bilinear supersymmetry-breaking
parameters, and between the gravitino and scalar masses. Finally, we discuss
models with non-universal supersymmetry-breaking contributions to Higgs masses,
and models in which the supersymmetry-breaking parameters are universal at some
scale below that of grand unification.
http://cambridge.org/us/catalogue/catalogue.asp?isbn=9780521763684 | Dark matter from dark energy-baryonic matter couplings: We present a scenario in which a scalar field dark energy is coupled to the
trace of the energy momentum tensor of the baryonic matter fields. In the
slow-roll regime, this interaction could give rise to the cosmological features
of dark matter. We work out the cosmological background solutions and fit the
parameters of the model using the Union 2 supernovae data set. Then, we develop
the cosmological perturbations up to linear order, and we find that the
perturbed variables have an acceptable behavior, in particular the density
contrast of baryonic matter grows similar to that in the $\Lambda$CDM model for
a suitable choice of the strength parameter of the coupling. |
General Relativistic corrections in density-shear correlations: We investigate the corrections which relativistic light-cone computations
induce on the correlation of the tangential shear with galaxy number counts,
also known as galaxy-galaxy lensing. The standard-approach to galaxy-galaxy
lensing treats the number density of sources in a foreground bin as observable,
whereas it is in reality unobservable due to the presence of relativistic
corrections. We find that already in the redshift range covered by the DES
first year data, these currently neglected relativistic terms lead to a
systematic correction of up to 50% in the density-shear correlation function
for the highest redshift bins. This correction is dominated by the the fact
that a redshift bin of number counts does not only lens sources in a background
bin, but is itself again lensed by all masses between the observer and the
counted source population. Relativistic corrections are currently ignored in
the standard galaxy-galaxy analyses, and the additional lensing of a counted
source populations is only included in the error budget (via the covariance
matrix). At increasingly higher redshifts and larger scales, these relativistic
and lensing corrections become however increasingly more important, and we here
argue that it is then more efficient, and also cleaner, to account for these
corrections in the density-shear correlations. | Relaxation in N-body simulations of disk galaxies: I use N-body simulations with two mass species of particles to demonstrate
that disk galaxy simulations are subject to collisional relaxation at a higher
rate than is widely assumed. Relaxation affects the vertical thickness of the
disk most strongly, and drives the velocity ellipsoid to a moderately flattened
shape similar to that observed for disk stars in the solar neighborhood. The
velocity ellipsoid in simulations with small numbers of particles quickly
approaches this shape, but shot noise also dominates the in-plane behavior.
Simulations with higher, but reachable, numbers of particles relax slowly
enough to be considered collisionless, allowing the in-plane dispersions to
rise due to spiral activity without heating the vertical motions. Relaxation
may have affected many previously published simulations of the formation and
evolution of galaxy disks. |
Testing homogeneity with the fossil record of galaxies: The standard Friedmann model of cosmology is based on the Copernican
Principle, i.e. the assumption of a homogeneous background on which structure
forms via perturbations. Homogeneity underpins both general relativistic and
modified gravity models and is central to the way in which we interpret
observations of the CMB and the galaxy distribution. It is therefore important
to probe homogeneity via observations. We describe a test based on the fossil
record of distant galaxies: if we can reconstruct key intrinsic properties of
galaxies as functions of proper time along their worldlines, we can compare
such properties at the same proper time for our galaxy and others. We achieve
this by computing the lookback time using radial Baryon Acoustic Oscillations,
and the time along galaxy world line using stellar physics, allowing us to
probe homogeneity, in principle anywhere inside the past light cone. Agreement
in the results would be an important consistency test -- although it would not
in itself prove homogeneity. Any significant deviation in the results however
would signal a breakdown of homogeneity. | New Constraints on the Early Expansion History: Cosmic microwave background measurements have pushed to higher resolution,
lower noise, and more sky coverage. These data enable a unique test of the
early universe's expansion rate and constituents such as effective number of
relativistic degrees of freedom and dark energy. Using the most recent data
from Planck and WMAP9, we constrain the expansion history in a model
independent manner from today back to redshift z=10^5. The Hubble parameter is
mapped to a few percent precision, limiting early dark energy and extra
relativistic degrees of freedom within a model independent approach to 2-16%
and 0.71 equivalent neutrino species respectively (95% CL). Within dark
radiation, barotropic aether, and Doran-Robbers models, the early dark energy
constraints are 3.3%, 1.9%, 1.2% respectively. |
RX J1548.9+0851, a fossil cluster?: Fossil galaxy groups are spatially extended X-ray sources with X-ray
luminosities above L_X,bol > 10^42 h_50^-2 ergs s^-1 and a central elliptical
galaxy dominating the optical, the second-brightest galaxy being at least 2
magnitudes fainter in the R band. Whether these systems are a distinct class of
objects resulting from exceptional formation and evolution histories is still
unclear, mainly due to the small number of objects studied so far, mostly
lacking spectroscopy of group members for group membership confirmation and a
detailed kinematical analysis. To complement the scarce sample of
spectroscopically studied fossils down to their faint galaxy populations, the
fossil candidate RX J1548.9+0851 (z=0.072) is studied in this work. Our results
are compared with existing data from fossils in the literature. We use ESO VLT
VIMOS multi-object spectroscopy to determine redshifts of the faint galaxy
population and study the luminosity-weighted dynamics and luminosity function
of the system. The full-spectrum fitting package ULySS is used to determine
ages and metallicities of group members. VIMOS imaging data are used to study
the morphology of the central elliptical. We identify 40 group members
spectroscopically within the central ~300 kpc of the system and find 31
additional redshifts from the literature, resulting in a total number of 54
spectroscopically confirmed group members within 1 Mpc. RX J1548.9+0851 is made
up of two bright ellipticals in the central region with a magnitude gap of
m_1,2 = 1.34 in the SDSS r' band leaving the definition of RX J1548.9+0851
being a fossil to the assumption of the virial radius. We find a
luminosity-weighted velocity dispersion of 568 km s^-1 and a mass of ~2.5 x
10^14 M_sun for the system confirming previous studies that revealed fossils to
be massive. (abridged) | Distance to the SMC from eclipsing binaries: The preliminary distance to a long period eclipsing binary in the Small
Magellanic Cloud SMC108.1.14904 is presented. The binary system contains two
non-active G-type bright giants. The orbital period is 185 days and the orbit
is circular. Using surface brightness calibration we calculated distance
modulus to the system (m-M)= 19.02 +/- 0.04 (stat.) +/- 0.05 (syst.) mag, where
systematic error is dominated by uncertainty of surface brightness calibration.
This is a second eclipsing binary in the SMC analysed by our team. |
Probing wave-optics effects and dark-matter subhalos with lensing of
gravitational waves from massive black holes: The Laser Interferometer Space Antenna (LISA) will detect gravitational waves
(GWs) emitted by massive black hole binaries (MBHBs) in the low-frequency
($\sim$mHz) band. Low-mass lenses, such as dark-matter (DM) subhalos, have
sizes comparable to the wavelength of these GWs. Encounters with these lenses
produce wave-optics (WO) effects that alter waveform phase and amplitude. Thus,
a single event with observable WO effects can be used to probe the lens
properties. In this paper, we first compute the probability of observing WO
effects in a model-agnostic way. We perform parameter estimation over
approximately 1000 MBHBs with total mass, mass ratio, and redshift spanning the
ranges relevant to LISA. We then calculate lensing rates using three
semi-analytical models of MBHB populations. In both cases, we use a waveform
model that includes merger, ringdown, and higher-order modes. We use two lens
population models: the theory-based Press-Schechter halo mass function and an
observation-based model derived from Sloan Digital Sky Survey, called the
measured velocity function. We find that the probability of detecting WO
effects can be as large as $\sim 3\%$, $\sim1.5\%$, and $\sim 1 \%$ at
$1\sigma$, $3\sigma$, and $5\sigma$ confidence levels, respectively. The most
optimistic MBHB population model yields $\sim 8$, $\sim 4$, and $\sim 3$ events
at the same confidence levels, while the rates drop to $\sim 0.01$ in the more
pessimistic scenarios. The most likely lens masses probed by LISA are in the
range $(10^3, 10^8)\, M_{\odot}$, and the most probable redshifts are in the
range $(0.3, 1.7)$. Therefore, LISA observations of WO effects can probe DM
subhalos, complementing strong lensing and other observations. | Planck 2015 results. XII. Full Focal Plane simulations: We present the 8th Full Focal Plane simulation set (FFP8), deployed in
support of the Planck 2015 results. FFP8 consists of 10 fiducial mission
realizations reduced to 18144 maps, together with the most massive suite of
Monte Carlo realizations of instrument noise and CMB ever generated, comprising
$10^4$ mission realizations reduced to about $10^6$ maps. The resulting maps
incorporate the dominant instrumental, scanning, and data analysis effects;
remaining subdominant effects will be included in future updates. Generated at
a cost of some 25 million CPU-hours spread across multiple
high-performance-computing (HPC) platforms, FFP8 is used for the validation and
verification of analysis algorithms, as well as their implementations, and for
removing biases from and quantifying uncertainties in the results of analyses
of the real data. |
A Census of Star-Forming Galaxies in the z~9-10 Universe based on
HST+Spitzer Observations Over 19 CLASH clusters: Three Candidate z~9-10
Galaxies and Improved Constraints on the Star Formation Rate Density at z~9: We utilise a two-color Lyman-Break selection criterion to search for z~9-10
galaxies over the first 19 clusters in the CLASH program. A systematic search
yields three z~9-10 candidates. While we have already reported the most robust
of these candidates, MACS1149-JD, two additional z~9 candidates are also found
and have H_{160}-band magnitudes of ~26.2-26.9. A careful assessment of various
sources of contamination suggests <~1 contaminants for our z~9-10 selection. To
determine the implications of these search results for the LF and SFR density
at z~9, we introduce a new differential approach to deriving these quantities
in lensing fields. Our procedure is to derive the evolution by comparing the
number of z~9-10 galaxy candidates found in CLASH with the number of galaxies
in a slightly lower redshift sample (after correcting for the differences in
selection volumes), here taken to be z~8. This procedure takes advantage of the
fact that the relative volumes available for the z~8 and z~9-10 selections
behind lensing clusters are not greatly dependent on the details of the lensing
models. We find that the normalization of the UV LF at z~9 is just
0.28_{-0.20}^{+0.39}\times that at z~8, ~1.4_{-0.8}^{+3.0}x lower than
extrapolating z~4-8 LF results. While consistent with the evolution in the UV
LF seen at z~4-8, these results marginally favor a more rapid evolution at z>8.
Compared to similar evolutionary findings from the HUDF, our result is less
insensitive to large-scale structure uncertainties, given our many independent
sightlines on the high-redshift universe. | Cosmological Dark Matter: a Review (the April Fool Edition): Evidence has continued to accumulate over the last few decades as to the
existence and nature of dark matter. Depending on the particle candidate, the
dark matter can exhibit one of several cosmologically defined models: hot dark
matter, cold dark matter, warm dark matter, self-interacting dark matter, and
fuzzy dark matter. In this paper I review the relevance and status of these
models, whether it is possible for more than one of these models to each
constitute some fraction of the dark matter, and discuss the prospects for
determining if any of these models can successfully describe the properties and
evolution of our own Universe. |
The 617 MHz - $λ$ 850 $μ$m Correlation (Cosmic Rays and Cold
Dust) in NGC 3044 and NGC 4157: We present the first maps of NGC 3044 and NGC 4157 at $\lambda\,450 \mu$m and
$\lambda\,850 \mu$m from the JCMT as well as the first maps at 617 MHz from the
GMRT. High latitude emission has been detected in both the radio continuum and
sub-mm for NGC 3044 and in the radio continuum for NGC 4157, including several
new features. The dust spectrum at long wavelengths required fitting with a
two-temperature model for both galaxies, implying the presence of cold dust.
Dust masses are $M_d\,=\,1.6\,\times\,10^8 M_\odot$ and
$M_d\,=\,2.1\,\times\,10^7 M_\odot$ for NGC 3044 and NGC 4157, respectively,
and are dominated by the cold component. There is a clear correlation between
the 617 MHz and $\lambda\,850 \mu$m emission in the two galaxies. In the case
of NGC 3044, this implies a relation between the non-thermal synchrotron
emission and cold dust. The 617 MHz component represents an integration of
massive star formation over the past $10^{7-8}$ yr and the $\lambda \,850 \mu$m
emission represents heating from the diffuse interstellar radiation field
(ISRF). The 617 MHz -- $\lambda\,850 \mu$m correlation improves when a
smoothing kernel is applied to the $\lambda\,850 \mu$m data to account for
differences between the CR electron diffusion scale and the mean free path of
an ISRF photon to dust. The best-fit relation is $L_{617_{\rm
MHz}}\,\propto\,{L_{850 \mu{\rm m}}}^{2.1\,\pm\,0.2}$ for NGC 3044. If
variations in the cold dust emissivity are dominated by variations in dust
density, and the synchrotron emission depends on magnetic field strength (a
function of gas density) as well as CR electron generation (a function of
massive star formation rate and therefore density via the Schmidt law) then the
expected correlation for NGC 3044 is $L_{617_{\rm MHz}}\,\propto\,{L_{850
\mu{\rm m}}}^{2.2}$, in agreement with the observed correlation. | A Synthetic Roman Space Telescope High-Latitude Time-Domain Survey:
Supernovae in the Deep Field: NASA will launch the Nancy Grace Roman Space Telescope (Roman) in the second
half of this decade, which will allow for a generation-defining measurement of
dark energy through multiple probes, including Type Ia supernovae (SNe Ia). To
improve decisions on survey strategy, we have created the first simulations of
realistic Roman images that include artificial SNe Ia injected as point sources
in the images. Our analysis combines work done on Roman simulations for weak
gravitational lensing studies as well as catalog-level simulations of SN
samples. We have created a time series of images over two years containing
$\sim$ 1,050 SNe Ia, covering a 1 square degree subarea of a planned 5 square
degree deep survey. We have released these images publicly for community use
along with input catalogs of all injected sources. We create secondary products
from these images by generating coadded images and demonstrating recovery of
transient sources using image subtraction. We perform first-use analyses on
these images in order to measure galaxy-detection efficiency, point
source-detection efficiency, and host-galaxy association biases. The simulated
images can be found here:
https://roman.ipac.caltech.edu/sims/SN_Survey_Image_sim.html. |
Nucleosynthesis Constraints on a Massive Gravitino in Neutralino Dark
Matter Scenarios: The decays of massive gravitinos into neutralino dark matter particles and
Standard Model secondaries during or after Big-Bang nucleosynthesis (BBN) may
alter the primordial light-element abundances. We present here details of a new
suite of codes for evaluating such effects, including a new treatment based on
PYTHIA of the evolution of showers induced by hadronic decays of massive,
unstable particles such as a gravitino. We also develop an analytical treatment
of non-thermal hadron propagation in the early universe, and use this to derive
analytical estimates for light-element production and in turn on decaying
particle lifetimes and abundances. We then consider specifically the case of an
unstable massive gravitino within the constrained minimal supersymmetric
extension of the Standard Model (CMSSM). We present upper limits on its
possible primordial abundance before decay for different possible gravitino
masses, with CMSSM parameters along strips where the lightest neutralino
provides all the astrophysical cold dark matter density. We do not find any
CMSSM solution to the cosmological Li7 problem for small m_{3/2}. Discounting
this, for m_{1/2} ~ 500 GeV and tan beta = 10 the other light-element
abundances impose an upper limit m_{3/2} n_{3/2}/n_\gamma < 3 \times 10^{-12}
GeV to < 2 \times 10^{-13} GeV for m_{3/2} = 250 GeV to 1 TeV, which is similar
in both the coannihilation and focus-point strips and somewhat weaker for tan
beta = 50, particularly for larger m_{1/2}. The constraints also weaken in
general for larger m_{3/2}, and for m_{3/2} > 3 TeV we find a narrow range of
m_{3/2} n_{3/2}/n_\gamma, at values which increase with m_{3/2}, where the Li7
abundance is marginally compatible with the other light-element abundances. | Are ultracompact minihalos really ultracompact?: Ultracompact minihalos (UCMHs) have emerged as a valuable probe of the
primordial power spectrum of density fluctuations at small scales. UCMHs are
expected to form at early times in regions with ${\delta\rho/\rho \gtrsim
10^{-3}}$, and they are theorized to possess an extremely compact ${\rho\propto
r^{-9/4}}$ radial density profile, which enhances their observable signatures.
Nonobservation of UCMHs can thus constrain the primordial power spectrum. Using
$N$-body simulations to study the collapse of extreme density peaks at ${z
\simeq 1000}$, we show that UCMHs forming under realistic conditions do not
develop the ${\rho\propto r^{-9/4}}$ profile and instead develop either
${\rho\propto r^{-3/2}}$ or ${\rho\propto r^{-1}}$ inner density profiles
depending on the shape of the power spectrum. We also demonstrate via idealized
simulations that self-similarity---the absence of a scale length---is necessary
to produce a halo with the ${\rho\propto r^{-9/4}}$ profile, and we argue that
this implies such halos cannot form from a Gaussian primordial density field.
Prior constraints derived from UCMH nonobservation must be reworked in light of
this discovery. Although the shallower density profile reduces UCMH visibility,
our findings reduce their signal by as little as $\mathcal O(10^{-2})$ while
allowing later-forming halos to be considered, which suggests that new
constraints could be significantly stronger. |
Giant Molecular Clouds in the Local Group Galaxy M33: We present an analysis of the systematic CO(2-1) survey at 12" resolution
covering most of the local group spiral M 33 which, at a distance of 840 kpc,
is close enough that individual giant molecular clouds (GMCs) can be
identified. The goal of this work is to study the properties of the GMCs in
this subsolar metallicity galaxy. The CPROPS (Cloud Properties) algorithm
(Rosolowsky & Leroy 2006) was used to identify 337 GMCs in M 33, the largest
sample to date in an external galaxy. The sample is used to study the GMC
luminosity function, or mass spectrum under the assumption of a constant
N(H2)/ICO ratio. We find that n(L)dL = K*L^(-2.0\pm0.1) for the entire sample.
However, when the sample is divided into inner and outer disk samples, the
exponent changes from 1.6 \pm 0.2 for the centre 2 kpc to 2.3 \pm 0.2 for
galactocentric distances larger than 2 kpc. Based on the emission in the FUV,
Halpha, 8mu, and 24mu bands, each cloud was classified in terms of its star
forming activity - no star formation, embedded, or exposed star formation
(visible in FUV and Halpha). At least one sixth of the clouds had no (massive)
star formation, suggesting that the average time required for star formation to
start is about one sixth of the total time for which the object is identifiable
as a GMC. The clouds without star formation have significantly lower CO
luminosities than those with star formation, whether embedded or exposed,
presumably related to the lack of heating sources. Taking the cloud sample as a
whole, the main non-trivial correlation was the decrease in cloud CO brightness
(or luminosity) with galactocentric radius. The complete cloud catalog,
including CO and HI spectra and the CO contours on the FUV, Halpha, 8mu, and
24mu images is presented in the appendix. | The Ultraluminous State: (Abridged) We revisit the question of the nature of ULXs through a detailed
investigation of their spectral shape, using the highest quality X-ray data
available in the XMM-Newton public archives. We confirm that simple spectral
models commonly used for the analysis and interpretation of ULXs (power-law
continuum and multi-colour disc blackbody models) are inadequate in the face of
such high quality data. Instead we find two near ubiquitous features in the
spectrum: a soft excess and a roll-over in the spectrum at energies above 3keV.
We investigate a range of more physical models to describe these data. We find
that disc plus Comptonised corona models fit the data well, but the derived
corona is cool, and optically thick (tau ~ 5-30). We argue that these observed
disc temperatures are not a good indicator of the black hole mass as the
powerful, optically thick corona drains energy from the inner disc, and
obscures it. We estimate the intrinsic (corona-less) disc temperature, and
demonstrate that in most cases it lies in the regime of stellar mass black
holes. These objects have spectra which range from those similar to the highest
mass accretion rate states in Galactic binaries, to those which clearly have
two peaks, one at energies below 1 keV (from the outer, unComptonised disc) and
one above 3 keV (from the Comptonised, inner disc). However, a few ULXs have a
significantly cooler corrected disc temperature; we suggest that these are the
most extreme stellar mass black hole accretors, in which a massive wind
completely envelopes the inner disc regions, creating a cool photosphere. We
conclude that ULXs provide us with an observational template for the transition
between Eddington and super-Eddington accretion flows, with the latter
occupying a new ultraluminous accretion state. |
Correlating Fourier phase information with real-space higher order
statistics: We establish for the first time heuristic correlations between harmonic space
phase information and higher order statistics. Using the spherical full-sky
maps of the cosmic microwave background as an example we demonstrate that known
phase correlations at large spatial scales can gradually be diminished when
subtracting a suitable best-fit (Bianchi-) template map of given strength. The
weaker phase correlations lead in turn to a vanishing signature of anisotropy
when measuring the Minkowski functionals and scaling indices in real-space and
comparing them with surrogate maps being free of phase correlations. Those
investigations can open a new road to a better understanding of signatures of
non-Gaussianities in complex spatial structures by elucidating the meaning of
Fourier phase correlations and their influence on higher order statistics. | Probing the origin of extragalactic magnetic fields with Fast Radio
Bursts: The joint analysis of the Dispersion and Faraday Rotation Measure from
distant, polarised Fast Radio Bursts may be used to put constraints on the
origin and distribution of extragalactic magnetic fields on cosmological
scales. While the combination of Dispersion and Faraday Rotation Measure can in
principle give the average magnetic fields along the line-of-sight, in practice
this method must be used with care because it strongly depends on the assumed
magnetisation model on large cosmological scales. Our simulations show that the
observation of Rotation Measures with $\geq 1-10 ~\rm rad/m^2$ in $\sim 10^2$
Fast Radio Bursts will be able to discriminate between extreme scenarios for
the origin of cosmic magnetic fields, independent of the exact distribution of
sources with redshift. This represent a strong case for incoming (e.g. ALERT,
CHIME) and future (e.g. with the Square Kilometer Array) radio polarisation
surveys of the sky. |
Can accelerated expansion of the universe be due to spacetime vorticity?: We present here a general relativistic mechanism for accelerated cosmic
expansion and the Hubble's constant. It is shown that spacetime vorticity
coupled to the magnetic field density in galaxies causes the galaxies to recede
from one another at a rate equal to the Hubble's constant. We therefore predict
an oscillatory universe, with zero curvature, without assuming violation of
Newtonian gravity at large distances or invoking dark energy/dark matter
hypotheses. The value of the Hubble's constant, along with the scale of
expansion, as well as the high isotropy of CMB radiation are deduced from the
model. | Consistency relations for large-scale structure in modified gravity and
the matter bispectrum: We study perturbation theory for large-scale structure in the most general
scalar-tensor theories propagating a single scalar degree of freedom, which
include Horndeski theories and beyond. We model the parameter space using the
effective field theory of dark energy. For Horndeski theories, the
gravitational field and fluid equations are invariant under a combination of
time-dependent transformations of the coordinates and fields. This symmetry
allows one to construct a physical adiabatic mode which fixes the
perturbation-theory kernels in the squeezed limit and ensures that the
well-known consistency relations for large-scale structure, originally derived
in general relativity, hold in modified gravity as well. For theories beyond
Horndeski, instead, one generally cannot construct such an adiabatic mode.
Because of this, the perturbation-theory kernels are modified in the squeezed
limit and the consistency relations for large-scale structure do not hold. We
show, however, that the modification of the squeezed limit depends only on the
linear theory. We investigate the observational consequences of this violation
by computing the matter bispectrum. In the squeezed limit, the largest effect
is expected when considering the cross-correlation between different tracers.
Moreover, the individual contributions to the 1-loop matter power spectrum do
not cancel in the infrared limit of the momentum integral, modifying the power
spectrum on non-linear scales. |
Topological Inflation with Large Tensor-to-scalar Ratio: BICEP2's detection on the primordial B-mode of CMB polarization suggests that
inflation occurred around GUT scale, with the tensor-to-scalar ratio r~0.2.
Inspired by this discosvery, we study the topological inflation which was
driven by a double/single/no well potential. We show that with proper choice of
parameters, all these three types of topological inflationary models could be
consistent with the constraints from current observations. | Chemical evolution of local galaxies in a hierarchical model: We investigate the chemical properties of local galaxies within a
cosmological framework in the hierarchical picture of galaxy formation. To this
aim, we use a hierarchical semi-analytic model which includes the contribution
from (i) low and intermediate mass stars, (ii) type Ia Supernovae (SNe) and
(iii) massive stars. - Abridged - We compare our predictions with available
observations in the Milky Way (MW), in local dwarf galaxies and in local
ellipticals. For Milky-Way-like galaxies, we can successfully reproduce the
[O-Fe] vs [Fe/H] relation observed in disc stars and the stellar metallicity
distribution (SMD). For dwarf galaxies, the stellar metallicity vs mass
relation is reproduced by assuming that a substantial fraction of the heavy
elements is lost through metal-enhanced outflows and a type Ia SN realization
probability lower than the one of MW-like galaxies. - Abridged - In
ellipticals, the observations indicate higher [alpha/Fe] values in larger
galaxies. - Abridged - Our results computed with a standard Salpeter initial
mass function (IMF) indicate a flat [alpha/Fe]-sigma relation. However, we
suggest a possible solution to this problem and show how, by assuming a star
formation-dependent IMF with a slope x=1.35 in systems with star formation
rates < 100 M_sun/yr and slightly flatter (i.e. with x=1) in object with
stronger star formation, the observed correlation between [alpha/Fe] and sigma
can be accounted for on a large velocity dispersion range. Fundamental roles
are played also by interaction-triggered starbursts and AGN. |
Modeling the distribution of Mg II absorbers around galaxies using
Background Galaxies & Quasars: We present joint constraints on the distribution of MgII absorption around
galaxies, by combining the MgII absorption seen in stacked background galaxy
spectra and the distribution of host galaxies of strong MgII systems from the
spectra of background quasars. We present a suite of models that predict, the
dependence of MgII absorption on a galaxy's apparent inclination, impact
parameter(b) and azimuthal angle. The variations in the absorption strength
with azimuthal angles provide much stronger constraints on the intrinsic
geometry of the MgII absorption than the dependence on the galaxy's
inclination. Strong MgII absorbers (W_r(2796)>0.3) are asymmetrically
distributed in azimuth around their host galaxies:72% of the absorbers studied
and 100% of the close-in absorbers within b<35 kpc, are located within 50deg of
the host galaxy's projected minor axis. Composite models consisting either of a
simple bipolar component plus a spherical or disk component, or a single highly
softened bipolar distribution, can well represent the azimuthal dependencies
observed in both the datasets. Simultaneously fitting both datasets to the
composite model, bipolar cone is confined to 50deg of the minor axis and
contains 2/3 of the total MgII absorption. The single softened cone model has
an exponential fall off with azimuth with an exponential scale-length in
opening angle of 45deg. We conclude that the distribution of MgII gas at low
impact parameters is not the same as that found at high impact parameters. MgII
absorption within 40 kpc primarily arises from cool MgII gas entrained in
winds. Beyond 40 kpc, there is evidence for a more symmetric distribution,
significantly different from that closer into the galaxies. Here a significant
component appears aligned more with the disk and is possibly inflowing, perhaps
as part of a galactic fountain or the inflow of material from further out in
the system. | Primordial Perturbations in Einstein-Aether and BPSH Theories: We study the primordial perturbations generated during a stage of
single-field inflation in Einstein-aether theories. Quantum fluctuations of the
inflaton and aether fields seed long wavelength adiabatic and isocurvature
scalar perturbations, as well as transverse vector perturbations.
Geometrically, the isocurvature mode is the potential for the velocity field of
the aether with respect to matter. For a certain range of parameters, this mode
may lead to a sizable random velocity of the aether within the observable
universe. The adiabatic mode corresponds to curvature perturbations of
co-moving slices (where matter is at rest). In contrast with the standard case,
it has a non-vanishing anisotropic stress on large scales. Scalar and vector
perturbations may leave significant imprints on the cosmic microwave
background. We calculate their primordial spectra, analyze their contributions
to the temperature anisotropies, and formulate some of the phenomenological
constraints that follow from observations. These may be used to further tighten
the existing limits on the parameters for this class of theories. The results
for the scalar sector also apply to the extension of Horava gravity recently
proposed by Blas, Pujolas and Sibiriakov. |
The 2pt+: an enhanced 2 point correlation function: We introduce a new method for testing departure from isotropy of points on a
sphere based on an enhanced form of the two-point correlation function that we
named 2pt+. This method uses information from the two extra variables that
define the vector between two points on a sphere. We show that this is a
powerful method to test departure from isotropy of a distribution of points on
a sphere especially when the number of events is small. We apply the method to
a few examples in astronomy and discuss the relevance for limited datasets,
such as the case of ultra-high energy cosmic rays. | Reconstructing Horndeski theories from phenomenological modified gravity
and dark energy models on cosmological scales: Recently we have derived a set of mapping relations that enables the
reconstruction of the family of Horndeski scalar-tensor theories which
reproduce the background dynamics and linear perturbations of a given set of
effective field theory of dark energy coefficients. In this paper we present a
number of applications of this reconstruction. We examine the form of the
underlying theories behind different phenomenological parameterizations of
modified gravity and dark energy used in the literature, as well as examine
theories that exhibit weak gravity, linear shielding, and minimal
self-acceleration. Finally, we propose a new inherently stable parametrization
basis for modified gravity and dark energy models. |
A new infrared color criterion for the selection of 0<z<7 AGN:
application to deep fields and implications for JWST surveys: [Abridged] It is widely accepted that observations at mid-infrared (mid-IR)
wavelengths enable the selection of galaxies with nuclear activity, which may
not be revealed even in the deepest X-ray surveys. In this work new near- and
mid-IR color diagnostics are explored, aiming for improved efficiency - better
completeness and less contamination - in selecting AGN out to very high
redshifts. We restrict our study to the James Webb Space Telescope wavelength
range (0.6-27um). The criteria are created based on the predictions by
state-of-the-art galaxy and AGN templates covering a wide variety of galaxy
properties, and tested against control samples with deep multi-wavelength
coverage (ranging from the X-rays to radio frequencies). We show that the
colors Ks-[4.5], [4.5]-[8.0], and [8.0]-[24] are ideal as AGN/non-AGN
diagnostics at, respectively, z<~1, 1<~z<~2.5, and z>~2.5-3. However, when the
source redshift is unknown, these colors should be combined. We thus develop an
improved IR criterion (using Ks and IRAC bands, KI) as a new alternative at
z<~2.5. KI does not show improved completeness (50-60% overall) in comparison
to commonly used IRAC-based AGN criteria, but is less affected by non-AGN
contamination (revealing a >50-90% level of successful AGN selection). We also
propose KIM (using Ks, IRAC, and MIPS-24um bands, KIM), which aims to select
AGN hosts from local distances to as far back as the end of reionization
(0<z<~7) with reduced non-AGN contamination. However, the necessary
testing-constraints and the small control-sample sizes prevent the confirmation
of its improved efficiency at z<~2.5. Overall, KIM shows a ~30-40% completeness
and a >70-90% level of successful AGN selection. KI and KIM are built to be
reliable against a ~10-20% error in flux, are based on existing filters, and
are suitable for immediate use. | Observing patchy reionization with future CMB polarization experiments: We study the signal from patchy reionization in view of the future high
accuracy polarization measurements of the Cosmic Microwave Background (CMB). We
implement an extraction procedure of the patchy reionization signal analogous
to CMB lensing. We evaluate the signal to noise ratio (SNR) for the future
Stage IV (S4) CMB experiment. The signal has a broad peak centered on the
degree angular scales, with a long tail at higher multipoles. The CMB S4
experiment can effectively constrain the properties of reionization by
measuring the signal on degree scales. The signal amplitude depends on the
properties of the structure determining the reionization morphology. We
describe bubbles having radii distributed log-normally. The expected S/N is
sensitive to the mean bubble radius: $\bar{R}=5$ Mpc implies $S/N \approx 4$,
$\bar{R}=10$ Mpc implies $S/N \approx 20$. The spread of the radii distribution
strongly affects the integrated SNR, that changes by a factor of $10^2$ when
$\sigma_{lnr}$ goes from $\ln 2$ to $\ln3$. Future CMB experiments will thus
place important constraints on the physics of reionization. |
A Massive, Cooling-Flow-Induced Starburst in the Core of a Highly
Luminous Galaxy Cluster: In the cores of some galaxy clusters the hot intracluster plasma is dense
enough that it should cool radiatively in the cluster's lifetime, leading to
continuous "cooling flows" of gas sinking towards the cluster center, yet no
such cooling flow has been observed. The low observed star formation rates and
cool gas masses for these "cool core" clusters suggest that much of the cooling
must be offset by astrophysical feedback to prevent the formation of a runaway
cooling flow. Here we report X-ray, optical, and infrared observations of the
galaxy cluster SPT-CLJ2344-4243 at z = 0.596. These observations reveal an
exceptionally luminous (L_2-10 keV = 8.2 x 10^45 erg/s) galaxy cluster which
hosts an extremely strong cooling flow (dM/dt = 3820 +/- 530 Msun/yr). Further,
the central galaxy in this cluster appears to be experiencing a massive
starburst (740 +/- 160 Msun/yr), which suggests that the feedback source
responsible for preventing runaway cooling in nearby cool core clusters may not
yet be fully established in SPT-CLJ2344-4243. This large star formation rate
implies that a significant fraction of the stars in the central galaxy of this
cluster may form via accretion of the intracluster medium, rather than the
current picture of central galaxies assembling entirely via mergers. | Validating dark energy models using polarised Sunyaev-Zel'dovich effect
with large-angle CMB temperature and E-mode polarization anisotropies: The tomography of the polarized Sunyaev-Zeldvich effect due to free electrons
of galaxy clusters can be used to constrain the nature of dark energy because
CMB quadrupoles at different redshifts as the polarization source are sensitive
to the integrated Sachs-Wolfe effect. Here we show that the low multipoles of
the temperature and E-mode polarization anisotropies from the all-sky CMB can
improve the constraint further through the correlation between them and the CMB
quadrupoles viewed from the galaxy clusters. Using a Monte-Carlo simulation, we
find that low multipoles of the temperature and E-mode polarization
anisotropies potentially improve the constraint on the equation of state of
dark energy parameter by $\sim 17$ percent. |
Dark Energy Survey Year 1 Results: Cross-Correlation Redshifts in the
DES -- Calibration of the Weak Lensing Source Redshift Distributions: We present the calibration of the Dark Energy Survey Year 1 (DES Y1) weak
lensing source galaxy redshift distributions from clustering measurements. By
cross-correlating the positions of source galaxies with luminous red galaxies
selected by the redMaGiC algorithm we measure the redshift distributions of the
source galaxies as placed into different tomographic bins. These measurements
constrain any such shifts to an accuracy of $\sim0.02$ and can be computed even
when the clustering measurements do not span the full redshift range. The
highest-redshift source bin is not constrained by the clustering measurements
because of the minimal redshift overlap with the redMaGiC galaxies. We compare
our constraints with those obtained from $\texttt{COSMOS}$ 30-band photometry
and find that our two very different methods produce consistent constraints. | NANOGrav Signal from First-Order Confinement/Deconfinement Phase
Transition in Different QCD Matters: Recently, an indicative evidence of a stochastic process, reported by the
NANOGrav Collaboration based on the analysis of 12.5-year pulsar timing array
data which might be interpreted as a potential stochastic gravitational wave
signal, has aroused keen interest of theorists. The first-order color charge
confinement phase transition at the QCD scale could be one of the cosmological
sources for the NANOGrav signal. If the phase transition is flavor dependent
and happens sequentially, it is important to find that what kind of QCD matter
in which the first-order confinement/deconfinement phase transition happens is
more likely to be the potential source of the NANOGrav signal during the
evolution of the universe. In this paper, we would like to illustrate that the
NANOGrav signal could be generated from confinement/deconfinement transition in
either heavy static quarks with a zero baryon chemical potential, or quarks
with a finite baryon chemical potential. In contrast, the gluon confinement
could not possibly be the source for the NANOGrav signal according to the
current observation. Future observation will help to distinguish between
different scenarios. |
The growth of galactic bulges through mergers in LCDM haloes revisited.
I. Present-day properties: We use the Millennium I and II cosmological simulations to revisit the impact
of mergers in the growth of bulges in central galaxies in the LCDM scenario. We
seed galaxies within the growing CDM haloes using semi-empirical relations to
assign stellar and gaseous masses, and an analytic treatment to estimate the
transfer of stellar mass to the bulge of the remnant after a galaxy merger. We
find that this model roughly reproduces the observed correlation between the
bulge-to-total (B/T) mass ratio and stellar mass in present-day central
galaxies as well as their observed demographics, although low-mass B/T<0.1
(bulgeless) galaxies might be scarce relative to the observed abundance. In our
merger-driven scenario, bulges have a composite population made of (i) stars
acquired from infalling satellites, (ii) stars transferred from the primary
disc due to merger-induced perturbations, and (iii) newly formed stars in
starbursts triggered by mergers. We find that (i) and (ii) are the main
channels of mass assembly, with the first being dominant for massive galaxies,
creating large bulges with different stellar populations than those of the
inner discs, while the second is dominant for intermediate/low-mass galaxies
creating small bulges with similar stellar populations to the inner discs. We
associate the dominion of the first (second) channel to classical (pseudo)
bulges, and compare the predicted fractions to observations. We remark that our
treatment does not include other mechanisms of bulge growth such as intrinsic
secular disc instabilities or misaligned gas accretion. We find that the
evolution of the stellar and gaseous contents of the satellite as it moves
towards the central galaxy is a key ingredient in setting the morphology of the
remnant, and that a good match to the observed bulge demographics occurs when
this evolution proceeds closely to that of the central galaxy. | Gathering Galaxy Distances in Abundance with Roman Wide-Area Data: The extragalactic distance scale is fundamental to our understanding of
astrophysics and cosmology. In recent years, the surface brightness fluctuation
(SBF) method, applied in the near-IR, has proven especially powerful for
measuring galaxy distances, first with HST and now with a new JWST program to
calibrate the method directly from the tip of the red giant branch (TRGB). So
far, however, the distances from space have been gathered slowly, one or two at
a time. With the Roman Space Telescope, we have the opportunity to measure
uniformly high-quality SBF distances to thousands of galaxies out to hundreds
of Mpc. The impact of these data on cosmology and galaxy studies depends on the
specifics of the survey, including the filter selection, exposure depth, and
(especially) the sky coverage. While the baseline HLWAS survey in four filters
plus the grism would yield useful data, the impact would be limited by the
relatively small area. A more optimal approach would concentrate on the most
efficient passband (F146), adopt an exposure time sufficient to measure good
quality distances well out into the Hubble flow, and then maximize the sky
coverage within the total time constraints. Grism observations over the same
area can provide the needed information on redshifts and spectral energy
distributions for compact sources, while colors for larger objects can be
obtained from lower resolution surveys. The proposed plan will enable accurate
determination of the physical properties of thousands of nearby galaxies, an
independent measure of the Hubble constant $H_0$ with negligible statistical
error, and competitive constraints on $S_8{\,=\,}\sigma_8(\Omega_m/0.3)^{0.5}$.
The resulting data set will be a phenomenal resource for a wide range of
studies in astrophysics and cosmology. |
SCORCH. III. Analytical Models of Reionization with Varying Clumping
Factors: In the Simulations and Constructions of the Reionization of Cosmic Hydrogen
(SCORCH) project, we compare analytical models of the hydrogen ionization
fraction with radiation-hydrodynamic simulations. We derive analytical models
of the mass-weighted hydrogen ionization fraction from the local ionization
balance equations as a more accurate alternative to the widely adopted model
based on the volume filling factor. In particular, our model has a
recombination term quadratic in the ionization fraction, which is consistent
with the two-body interaction nature of recombination. Then, we use the
radiation-hydrodynamic simulations to study the clumping factors needed to
solve the analytical equations, and provide accurate fitting functions. We find
that the ionized hydrogen clumping factors from our radiative transfer
simulations are significantly different than those from other simulations that
use a uniform photoionization background. In addition to redshift dependence,
we also see the dependence of ionized hydrogen clumping factor on ionization
fraction, and we incorporate this into our fits. We calculate the reionization
histories using our analytical models and clumping factors and compare with
widely adopted models, and all of our models achieve $<7\%$ difference from
simulation results while the other models have $>20\%$ deviations. The Thomson
optical depths from reionization calculated from our analytical models result
in $<5\%$ deviation from simulations, while the previous analytical models have
$>20\%$ difference in and could result in biased conclusions of the IGM
reionization. | Constrained Local UniversE Simulations: A Local Group Factory: Near field cosmology is practiced by studying the Local Group (LG) and its
neighbourhood. The present paper describes a framework for simulating the near
field on the computer. Assuming the LCDM model as a prior and applying the
Bayesian tools of the Wiener filter (WF) and constrained realizations of
Gaussian fields to the Cosmicflows-2 (CF2) survey of peculiar velocities,
constrained simulations of our cosmic environment are performed. The aim of
these simulations is to reproduce the LG and its local environment. Our main
result is that the LG is likely a robust outcome of the LCDM scenario when
subjected to the constraint derived from CF2 data, emerging in an environment
akin to the observed one. Three levels of criteria are used to define the
simulated LGs. At the base level, pairs of halos must obey specific isolation,
mass and separation criteria. At the second level the orbital angular momentum
and energy are constrained and on the third one the phase of the orbit is
constrained. Out of the 300 constrained simulations 146 LGs obey the first set
of criteria, 51 the second and 6 the third. The robustness of our LG factory
enables the construction of a large ensemble of simulated LGs. Suitable
candidates for high resolution hydrodynamical simulations of the LG can be
drawn from this ensemble, which can be used to perform comprehensive studies of
the formation of the LG |
Cosmologies with a time dependent vacuum: The idea that the cosmological term, Lambda, should be a time dependent
quantity in cosmology is a most natural one. It is difficult to conceive an
expanding universe with a strictly constant vacuum energy density, namely one
that has remained immutable since the origin of time. A smoothly evolving
vacuum energy density that inherits its time-dependence from cosmological
functions, such as the Hubble rate or the scale factor, is not only a
qualitatively more plausible and intuitive idea, but is also suggested by
fundamental physics, in particular by quantum field theory (QFT) in curved
space-time. To implement this notion, is not strictly necessary to resort to ad
hoc scalar fields, as usually done in the literature (e.g. in quintessence
formulations and the like). A "running" Lambda term can be expected on very
similar grounds as one expects (and observes) the running of couplings and
masses with a physical energy scale in QFT. Furthermore, the experimental
evidence that the equation of state of the dark energy could be evolving with
time/redshift (including the possibility that it might currently behave
phantom-like) suggests that a time-variable Lambda term (possibly accompanied
by a variable Newton's gravitational coupling G=G(t)) could account in a
natural way for all these features. Remarkably enough, a class of these models
(the "new cosmon") could even be the clue for solving the old cosmological
constant problem, including the coincidence problem. | Planck 2015 results. XV. Gravitational lensing: We present the most significant measurement of the cosmic microwave
background (CMB) lensing potential to date (at a level of 40 sigma), using
temperature and polarization data from the Planck 2015 full-mission release.
Using a polarization-only estimator we detect lensing at a significance of 5
sigma. We cross-check the accuracy of our measurement using the wide frequency
coverage and complementarity of the temperature and polarization measurements.
Public products based on this measurement include an estimate of the lensing
potential over approximately 70% of the sky, an estimate of the lensing
potential power spectrum in bandpowers for the multipole range 40<L<400 and an
associated likelihood for cosmological parameter constraints. We find good
agreement between our measurement of the lensing potential power spectrum and
that found in the best-fitting LCDM model based on the Planck temperature and
polarization power spectra. Using the lensing likelihood alone we obtain a
percent-level measurement of the parameter combination $\sigma_8
\Omega_m^{0.25} = 0.591\pm 0.021$. We combine our determination of the lensing
potential with the E-mode polarization also measured by Planck to generate an
estimate of the lensing B-mode. We show that this lensing B-mode estimate is
correlated with the B-modes observed directly by Planck at the expected level
and with a statistical significance of 10 sigma, confirming Planck's
sensitivity to this known sky signal. We also correlate our lensing potential
estimate with the large-scale temperature anisotropies, detecting a
cross-correlation at the 3 sigma level, as expected due to dark energy in the
concordance LCDM model. |
Early structure formation from primordial density fluctuations with a
blue-tilted power spectrum: While observations of large-scale structure and the cosmic microwave
background (CMB) provide strong constraints on the amplitude of the primordial
power spectrum (PPS) on scales larger than 10~Mpc, the amplitude of the power
spectrum on sub-galactic length scales is much more poorly constrained. We
study early structure formation in a cosmological model with a blue-tilted PPS.
We assume that the standard scale-invariant PPS is modified at small length
scales as $P(k) \sim k^{m_{\rm s}}$ with $m_{\rm s} > 1$. We run a series of
cosmological hydrodynamic simulations to examine the dependence of the
formation epoch and the characteristic mass of primordial stars on the tilt of
the PPS. In models with $m_{\rm s} > 1$, star-forming gas clouds are formed at
$z > 100$, when formation of hydrogen molecules is inefficient because the
intense CMB radiation destroys chemical intermediates. Without efficient
coolant, the gas clouds gravitationally contract while keeping a high
temperature. The protostars formed in such "hot" clouds grow very rapidly by
accretion to become extremely massive stars that may leave massive black holes
with a few hundred solar-masses at $z > 100$. The shape of the PPS critically
affects the properties and the formation epoch of the first generation of
stars. Future experiments of the CMB polarization and the spectrum distortion
may provide important information on the nature of the first stars and their
formation epoch, and hence on the shape of the small-scale power spectrum. | Constraints on primordial density perturbations from induced
gravitational waves: We consider the stochastic background of gravitational waves produced during
the radiation-dominated hot big bang as a constraint on the primordial density
perturbation on comoving length scales much smaller than those directly probed
by the cosmic microwave background or large-scale structure. We place weak
upper bounds on the primordial density perturbation from current data. Future
detectors such as BBO and DECIGO will place much stronger constraints on the
primordial density perturbation on small scales. |
On the use of black hole binaries as probes of local dark energy
properties: Accretion of dark energy onto black holes will take place when dark energy is
not a cosmological constant. It has been proposed that the time evolution of
the mass of the black holes in binary systems due to dark energy accretion
could be detectable by gravitational radiation. This would make it possible to
use observations of black hole binaries to measure local dark energy
properties, e.g., to determine the sign of 1+w where w is the dark energy
equation of state. In this Letter we show that such measurements are unfeasible
due to the low accretion rates. | The Halo Spin Transition as a Probe of Dark Energy: We present a numerical evidence supporting the claim that the mass-dependent
transitions of the halo spin orientations from the intermediate to the minor
principal directions of the local tidal fields can in principle be a useful
discriminator of dark energy models. We first define a spin transition zone as
the mass range of the halos, $\Delta m_{t}$, for which the intrinsic spin
alignments with the minor tidal principal directions become as strong as that
with the intermediate principal directions. Then, utilizing the halo samples
from the DEUS simulations performed separately for the WMAP7 $\Lambda$CDM,
phantom DE and quintessence models, we investigate if and how the three
different dark energy models differ in $\Delta m_{t}$. It is shown that the
differences in $\Delta m_{t}$ among the three dark energy models are
significant enough to discriminate the models from one another and robust
against the variations of the smoothing scale of the tidal field and redshift.
Noting that a narrower spin transition zone is more powerful as a probe of dark
energy, we also show that the spin transition zones become narrower at higher
redshifts, in the filamentary environments and for the case that the tidal
fields are smoothed on the smaller scales. Our result is consistent with the
scenario that $\Delta m_{t}$ is mainly determined by how fast the nonlinear
evolution of the tidal field proceeds, which in turn sensitively depends on the
background cosmology. |
Galaxy clusters, cosmic chronometers and the Einstein equivalence
principle: The Einstein equivalence principle in the electromagnetic sector can be
violated in modifications of gravity theory generated by a multiplicative
coupling of a scalar field to the electromagnetic Lagrangian. In such theories,
deviations of the standard result for the cosmic distance duality relation, and
a variation of the fine structure constant are expected and are unequivocally
intertwined. In this paper, we search for these possible cosmological
signatures by using galaxy cluster gas mass fraction measurements and cosmic
chronometers. No significant departure from general relativity is found
regardless of our assumptions about cosmic curvature or a possible depletion
factor evolution in cluster measurements. | The dependence of star formation activity on environment and stellar
mass at z~1 from the HiZELS H-alpha survey: (Abridged) This paper presents an environment and stellar mass study of a
large sample of star-forming (SF) galaxies at z=0.84 from the HiZELS survey,
over 1.3 deg^2 in the COSMOS and UKIDSS UDS fields. By taking advantage of a
truly panoramic coverage, from the field to a rich cluster, it is shown that
both mass and environment play crucial roles in determining the properties of
SF galaxies. The median specific SFR declines with mass in all environments,
and the fraction of galaxies forming stars declines from ~40%, for M~10^10M_sun
to effectively zero at M>10^11.5M_sun, confirming that mass-downsizing is
generally in place by z~1. The fraction of SF galaxies also falls as a function
of local environmental density from ~40% in the field to approaching zero at
rich group/cluster densities. When SF does occur in high density regions, it is
merger-dominated and, if only non-merging SF galaxies are considered, then the
environment and mass trends are even stronger and largely independent, as in
the local Universe. The median SFR of SF galaxies is found to increase with
density up to intermediate (group or cluster outskirts) densities; this is
clearly seen as a change in the faint-end slope of the H-alpha LF from steep
(-1.9), in poor fields, to shallow (-1.1) in groups and clusters.
Interestingly, the relation between median SFR and environment is only found
for low to moderate-mass galaxies (below ~10^10.6M_sun), and is not seen for
massive SF galaxies. Overall, these observations provide a detailed view over a
sufficiently large range of mass and environment to reconcile previous
observational claims: mass is the primary predictor of SF activity at z~1, but
the environment, while enhancing the median SFR of (lower-mass) SF galaxies, is
ultimately responsible for suppressing SF activity in all galaxies above
surface densities of 10-30 Mpc^-2 (groups and clusters). |
The Lyman-alpha signature of the first galaxies: We present the Cosmic Lyman-$\alpha$ Transfer code (COLT), a massively
parallel Monte-Carlo radiative transfer code, to simulate Lyman-$\alpha$
(Ly$\alpha$) resonant scattering through neutral hydrogen as a probe of the
first galaxies. We explore the interaction of centrally produced Ly$\alpha$
radiation with the host galactic environment. Ly$\alpha$ photons emitted from
the luminous starburst region escape with characteristic features in the line
profile depending on the density distribution, ionization structure, and bulk
velocity fields. For example, anisotropic ionization exhibits a tall peak close
to line centre with a skewed tail that drops off gradually. Idealized models of
first galaxies explore the effect of mass, anisotropic H II regions, and
radiation pressure driven winds on Ly$\alpha$ observables. We employ mesh
refinement to resolve critical structures. We also post-process an ab initio
cosmological simulation and examine images captured at various escape distances
within the 1 Mpc$^3$ comoving volume. Finally, we discuss the emergent spectra
and surface brightness profiles of these objects in the context of high-$z$
observations. The first galaxies will likely be observed through the red
damping wing of the Ly$\alpha$ line. Observations will be biased toward
galaxies with an intrinsic red peak located far from line centre that reside in
extensive H II super bubbles, which allows Hubble flow to sufficiently redshift
photons away from line centre and facilitate transmission through the
intergalactic medium (IGM). Even with gravitational lensing to boost the
luminosity this preliminary work indicates that Ly$\alpha$ emission from
stellar clusters within haloes of $M_{\rm vir}<10^9~{\rm M}_\odot$ is generally
too faint to be detected by the James Webb Space Telescope (JWST). | Planck 2013 results. XXVII. Doppler boosting of the CMB: Eppur si muove: Our velocity relative to the rest frame of the cosmic microwave background
(CMB) generates a dipole temperature anisotropy on the sky which has been well
measured for more than 30 years, and has an accepted amplitude of v/c =
0.00123, or v = 369km/s. In addition to this signal generated by Doppler
boosting of the CMB monopole, our motion also modulates and aberrates the CMB
temperature fluctuations (as well as every other source of radiation at
cosmological distances). This is an order 0.1% effect applied to fluctuations
which are already one part in roughly one hundred thousand, so it is quite
small. Nevertheless, it becomes detectable with the all-sky coverage, high
angular resolution, and low noise levels of the Planck satellite. Here we
report a first measurement of this velocity signature using the aberration and
modulation effects on the CMB temperature anisotropies, finding a component in
the known dipole direction, (l,b)=(264, 48) [deg], of 384km/s +- 78km/s (stat.)
+- 115km/s (syst.). This is a significant confirmation of the expected
velocity. |
Constraints on growth index parameters from current and future
observations: We use current and future simulated data of the growth rate of large scale
structure in combination with data from supernova, BAO, and CMB surface
measurements, in order to put constraints on the growth index parameters. We
use a recently proposed parameterization of the growth index that interpolates
between a constant value at high redshifts and a form that accounts for
redshift dependencies at small redshifts. We also suggest here another
exponential parameterization with a similar behaviour. The redshift dependent
parametrizations provide a sub-percent precision level to the numerical growth
function, for the full redshift range. Using these redshift parameterizations
or a constant growth index, we find that current available data from galaxy
redshift distortions and Lyman-alpha forests is unable to put significant
constraints on any of the growth parameters. For example both $\Lambda$CDM and
flat DGP are allowed by current growth data. We use an MCMC analysis to study
constraints from future growth data, and simulate pessimistic and moderate
scenarios for the uncertainties. In both scenarios, the redshift
parameterizations discussed are able to provide significant constraints and
rule out models when incorrectly assumed in the analysis. The values taken by
the constant part of the parameterizations as well as the redshift slopes are
all found to significantly rule out an incorrect background. We also find that,
for our pessimistic scenario, an assumed constant growth index over the full
redshift range is unable to rule out incorrect models in all cases. This is due
to the fact that the slope acts as a second discriminator at smaller redshifts
and therefore provide a significant test to identify the underlying gravity
theory. | Lambda-CDM and the WMAP power spectrum beam profile sensitivity: We first discuss the sensitivity of the WMAP CMB power spectrum to systematic
errors by calculating the raw CMB power spectrum from WMAP data. We find that
the power spectrum is surprisingly sensitive to the WMAP radiometer beam
profile even at the position of the first acoustic peak on ~1 degree scales.
Although the WMAP beam profile core is only 12.6arcmin FWHM at W, there is a
long power-law tail to the beam due to side-lobes and this causes significant
effects even at the first peak position. We then test the form of the
beam-profile used by the WMAP team which is based on observations of Jupiter.
We stacked radio source beam profiles as observed in each WMAP band and found
that they showed a wider profile in Q, V, W than the Jupiter profile. We have
now checked that this is not due to any Eddington or other bias in our sample
by showing that the same results are obtained when radio sources are selected
at 1.4GHz and that our methods retrieve the Jupiter beam when it is employed in
simulations. Finally, we show that the uncertainty in the WMAP beam profile
allows the position as well as the amplitude of the first peak to be changed
and how this could allow simpler cosmologies than standard Lambda-CDM to fit
the CMB data. |
Dark Energy Survey Year 3 Results: Measuring the Survey Transfer
Function with Balrog: We describe an updated calibration and diagnostic framework, Balrog, used to
directly sample the selection and photometric biases of the Dark Energy
Survey's (DES) Year 3 (Y3) dataset. We systematically inject onto the
single-epoch images of a random 20% subset of the DES footprint an ensemble of
nearly 30 million realistic galaxy models derived from DES Deep Field
observations. These augmented images are analyzed in parallel with the original
data to automatically inherit measurement systematics that are often too
difficult to capture with traditional generative models. The resulting object
catalog is a Monte Carlo sampling of the DES transfer function and is used as a
powerful diagnostic and calibration tool for a variety of DES Y3 science,
particularly for the calibration of the photometric redshifts of distant
"source" galaxies and magnification biases of nearer "lens" galaxies. The
recovered Balrog injections are shown to closely match the photometric property
distributions of the Y3 GOLD catalog, particularly in color, and capture the
number density fluctuations from observing conditions of the real data within
1% for a typical galaxy sample. We find that Y3 colors are extremely well
calibrated, typically within ~1-8 millimagnitudes, but for a small subset of
objects we detect significant magnitude biases correlated with large
overestimates of the injected object size due to proximity effects and
blending. We discuss approaches to extend the current methodology to capture
more aspects of the transfer function and reach full coverage of the survey
footprint for future analyses. | How does the cosmic web impact assembly bias?: The mass, accretion rate and formation time of dark matter haloes near
proto-filaments (identified as saddle points of the potential) are analytically
predicted using a conditional version of the excursion set approach in its
so-called "upcrossing" approximation. The model predicts that at fixed mass,
mass accretion rate and formation time vary with orientation and distance from
the saddle, demonstrating that assembly bias is indeed influenced by the tides
imposed by the cosmic web. Starved, early forming haloes of smaller mass lie
preferentially along the main axis of filaments, while more massive and younger
haloes are found closer to the nodes. Distinct gradients for distinct tracers
such as typical mass and accretion rate occur because the saddle condition is
anisotropic, and because the statistics of these observables depend on both the
conditional means and their covariances. The theory is extended to other
critical points of the potential field. The response of the mass function to
variations of the matter density field (the so-called large scale bias) is
computed, and its trend with accretion rate is shown to invert along the
filament. The signature of this model should correspond at low redshift to an
excess of reddened galactic hosts at fixed mass along preferred directions, as
recently reported in spectroscopic and photometric surveys and in
hydrodynamical simulations. The anisotropy of the cosmic web emerges therefore
as a significant ingredient to describe jointly the dynamics and physics of
galaxies, e.g. in the context of intrinsic alignments or morphological
diversity. |
Supervoid Origin of the Cold Spot in the Cosmic Microwave Background: We use a WISE-2MASS-Pan-STARRS1 galaxy catalog to search for a supervoid in
the direction of the Cosmic Microwave Background Cold Spot. We obtain
photometric redshifts using our multicolor data set to create a tomographic map
of the galaxy distribution. The radial density profile centred on the Cold Spot
shows a large low density region, extending over 10's of degrees. Motivated by
previous Cosmic Microwave Background results, we test for underdensities within
two angular radii, $5^\circ$, and $15^\circ$. Our data, combined with an
earlier measurement by Granett et al 2010, are consistent with a large $R_{\rm
void}=(192 \pm 15)h^{-1} Mpc $ $(2\sigma)$ supervoid with $\delta \simeq -0.13
\pm 0.03$ centered at $z=0.22\pm0.01$. Such a supervoid, constituting a
$\sim3.5 \sigma$ fluctuation in the $\Lambda CDM$ model, is a plausible cause
for the Cold Spot. | Cosmology with cosmic shear observations: a review: Cosmic shear is the distortion of images of distant galaxies due to weak
gravitational lensing by the large-scale structure in the Universe. Such images
are coherently deformed by the tidal field of matter inhomogeneities along the
line of sight. By measuring galaxy shape correlations, we can study the
properties and evolution of structure on large scales as well as the geometry
of the Universe. Thus, cosmic shear has become a powerful probe into the nature
of dark matter and the origin of the current accelerated expansion of the
Universe. Over the last years, cosmic shear has evolved into a reliable and
robust cosmological probe, providing measurements of the expansion history of
the Universe and the growth of its structure.
We review here the principles of weak gravitational lensing and show how
cosmic shear is interpreted in a cosmological context. Then we give an overview
of weak-lensing measurements, and present the main observational cosmic-shear
results since it was discovered 15 years ago, as well as the implications for
cosmology. We then conclude with an outlook on the various future surveys and
missions, for which cosmic shear is one of the main science drivers, and
discuss promising new weak cosmological lensing techniques for future
observations. |
Unifying dark matter, dark energy and inflation with a fuzzy dark fluid: Scalar fields appear in many cosmological models, in particular in order to
provide explanations for dark energy and inflation, but also to emulate dark
matter. In this paper, we show that it is possible for a scalar field to
replace simultaneously dark matter, dark energy and inflation by assuming the
existence of a non-minimal coupling to gravity, a Mexican hat potential, and a
spontaneous symmetry breaking before inflation. After inflation, the scalar
field behaves like a dark fluid, mimicking dark energy and dark matter, and has
a dark matter behaviour similar to fuzzy dark matter. | Most Submillimetre Galaxies are Major Mergers: We analyse subarcsecond resolution interferometric CO line data for twelve
sub-millimetre-luminous (S850um > 5mJy) galaxies with redshifts between 1 and
3, presenting new data for four of them. Morphologically and kinematically most
of the twelve systems appear to be major mergers. Five of them are
well-resolved binary systems, and seven are compact or poorly resolved. Of the
four binary systems for which mass measurements for both separate components
can be made, all have mass ratios of 1:3 or closer. Furthermore, comparison of
the ratio of compact to binary systems with that observed in local ULIRGs
indicates that at least a significant fraction of the compact SMGs must also be
late-stage mergers. In addition, the dynamical and gas masses we derive are
most consistent with the lower end of the range of stellar masses published for
these systems, favouring cosmological models in which SMGs result from mergers.
These results all point to the same conclusion, that likely most of the bright
SMGs with L_IR > 5x10e12L_sun are major mergers. |
Detecting Sub-lunar Mass Compact Objects toward the Local Group Galaxies: By monitoring a large number of stars in the Local Group galaxies, we can
detect nanolensing events by sub-lunar mass compact objects (SULCOs) such as
primordial black holes (PBHs) and rogue (free-floating) dwarf planets in the
Milky Way halo. In contarst to microlensing by stellar-mass objects, the
finite-source size effect becomes important and the lensing time duration
becomes shorter ($\sim 10^{1-4}\,\textrm{s}$). Using stars with $V<26$ in M33
as sources, for one-night observation, we would be able to detect $10^{3-4}$
nanolensing events caused by SULCOs in the Milky Way halo with a mass of
$10^{-9}M_{\odot}$ to $10^{-7}M_{\odot}$ for sources with S/N$>5$ if SULCOs
constitute all the dark matter components. Moreover, we expect $10^{1-2}$
events in which bright blue stars with S/N$>100$ are weakly amplified due to
lensing by SULCOs with a mass range of $10^{-11}M_{\odot}$ to
$10^{-9}M_{\odot}$. Thus the method would open a new window on SULCOs in the
Milky Way halo that would otherwise not be observable. | Testing the Etherington's distance duality relation at higher redshifts:
the combination of radio quasars and gravitational waves: In this paper we analyse the implications of the latest cosmological data
sets to test the Etherington's distance duality relation (DDR), which connects
the luminosity distance $D_L$ and angular diameter distance $D_A$ at the same
redshift. For $D_L$ we consider the simulated data of gravitational waves from
the third-generation gravitational wave detector (the Einstein Telescope, ET),
which can be considered as standard candles (or standard siren), while the
angular diameter distances $D_A$ are derived from the newly-compiled sample of
compact radio quasars observed by very-long-baseline interferometry (VLBI),
which represents a type of new cosmological standard ruler. Alleviating the
absorption and scattering effects of dust in the Universe, this will create a
valuable opportunity to directly test DDR at much higher precision with the
combination of gravitational wave (GW) and electromagnetic (EM) signals. Our
results show that, with the combination of the current radio quasar
observations, the duality-distance relation can be verified at the precision of
$10^{-2}$. Moreover, the Einstein Telescope ET would produce more robust
constraints on the validity of such distance duality relation (at the precision
of $10^{-3}$), with a larger sample of compact milliarcsecond radio quasars
detected in future VLBI surveys. |
The Atacama Cosmology Telescope: a measurement of the primordial power
spectrum: We present constraints on the primordial power spectrum of adiabatic
fluctuations using data from the 2008 Southern Survey of the Atacama Cosmology
Telescope (ACT). The angular resolution of ACT provides sensitivity to scales
beyond \ell = 1000 for resolution of multiple peaks in the primordial
temperature power spectrum, which enables us to probe the primordial power
spectrum of adiabatic scalar perturbations with wavenumbers up to k \simeq 0.2
Mpc^{-1}. We find no evidence for deviation from power-law fluctuations over
two decades in scale. Matter fluctuations inferred from the primordial
temperature power spectrum evolve over cosmic time and can be used to predict
the matter power spectrum at late times; we illustrate the overlap of the
matter power inferred from CMB measurements (which probe the power spectrum in
the linear regime) with existing probes of galaxy clustering, cluster
abundances and weak lensing constraints on the primordial power. This
highlights the range of scales probed by current measurements of the matter
power spectrum. | Cosmological gravitational particle production of massive spin-2
particles: The phenomenon of cosmological gravitational particle production (CGPP) is
expected to occur during the period of inflation and the transition into a hot
big bang cosmology. Particles may be produced even if they only couple directly
to gravity, and so CGPP provides a natural explanation for the origin of dark
matter. In this work we study the gravitational production of massive spin-2
particles assuming two different couplings to matter. We evaluate the full
system of mode equations, including the helicity-0 modes, and by solving them
numerically we calculate the spectrum and abundance of massive spin-2 particles
that results from inflation on a hilltop potential. We conclude that CGPP might
provide a viable mechanism for the generation of massive spin-2 particle dark
matter during inflation, and we identify the favorable region of parameter
space in terms of the spin-2 particle's mass and the reheating temperature. As
a secondary product of our work, we identify the conditions under which such
theories admit ghost or gradient instabilities, and we thereby derive a
generalization of the Higuchi bound to Friedmann-Robertson-Walker (FRW)
spacetimes. |
Dynamical Tidal Locking Theory: A new source of the Spin of Dark Matter
Halos: We revisit the question of what mechanism is responsible for the spins of
halos of dark matter. The answer to this question is of high importance for
modeling galaxy intrinsic alignment, which can potentially contaminate current
and future lensing data. In particular, we show that when the dark matter halos
pass nearly by each other in dense environments-- namely halo assemblies-- they
swing and spin each other via exerting mutual tidal torques. We show that this
has a significant contribution to the spin of dark matter halos comparable to
that of calculated by the so-called tidal torque theory (TTT). We use the
results of state-of-the-art simulation of Illutris to check the prediction of
this theory against the simulation data. | New H2O masers in Seyfert and FIR bright galaxies. III. The Southern
Sample: Recently, a relationship between the water maser detection rate and far
infrared (FIR) flux densities has been established as a result of two 22 GHz
maser surveys in a complete sample of galaxies (Dec>-30 degree) with 100 micron
flux densities of > 50 Jy and > 30 Jy. This survey has been extended to the
southern galaxies in order to discover new maser sources and to investigate the
galaxies hosting the maser spots with particular emphasis on their nuclear
regions. A sample of 12 galaxies with Dec<-30 degree and S(100 micron)>50 Jy
was observed with the 70-m telescope of the Canberra Deep Space Communication
Complex (CDSCC) at Tidbinbilla (Australia) in a search for water maser
emission. The average 3 sigma noise level of the survey is 15 mJy for a 0.42
km/s channel, corresponding to a detection threshold of ~0.1 solar luminosities
for the isotropic maser luminosity at a distance of 25 Mpc. Two new detections
are reported: a kilomaser with an isotropic luminosity L_H2O ~5 solar
luminosities in NGC3620 and a maser with about twice this luminosity in the
merger system NGC3256. The detections have been followed-up through continuum
and spectral line interferometric observations with the Australia Telescope
Compact Array (ATCA). In NGC3256, a fraction (about a third) of the maser
emission arises from two hot spots associated with star formation activity,
which are offset from the galactic nuclei of the system. The remaining emission
may arise from weaker centers of maser activity distributed over the central 50
arcsec. [abridged] |
Distance and Reddening of the Isolated Dwarf Irregular Galaxy NGC 1156: We present a photometric estimation of the distance and reddening values to
the dwarf irregular galaxy NGC 1156, which is one of the best targets to study
the isolated dwarf galaxies in the nearby universe. We have used the imaging
data sets of the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)
High Resolution Channel (HRC) of the central region of NGC 1156 (26" X 29")
available in the HST archive for this study. From the (U-B, B-V) color-color
diagram, we first estimate the total (foreground + internal) reddening toward
NGC 1156 of E(B-V) =0.35 +/- 0.05 mag, whereas only the foreground reddening
was previously known to be E(B-V)=0.16 mag (Burstein & Heiles) or 0.24 mag
(Schlegel, Finkbeiner, & Davis). Based on the brightest stars method, selecting
the three brightest blue supergiant (BSG) stars with mean B magnitude of
<B(3B)> = 21.94 mag and the three brightest red supergiant (RSG) stars with
mean V magnitude of <V(3R)> = 22.76 mag, we derive the distance modulus to NGC
1156 to be (m-M)_{0,BSG} = 29.55 mag and (m-M)_{0,RSG} = 29.16 mag. By using
weights of 1 and 1.5 for the distance moduli from using the BSGs and the RSGs,
respectively, we finally obtain the weighted mean distance modulus to NGC 1156
(m-M)_0 = 29.39 +/- 0.20 mag (d = 7.6 +/- 0.7 Mpc), which is in very good
agreement with the previous estimates. Combining the photometry data of this
study with those of Karachentsev et al. gives smaller distance to NGC 1156,
which is discussed together with the limits of the data. | Cosmology with the cluster mass function: mass estimators and shape
systematics in large weak lensing surveys: Accurate measurement of the cluster mass function is a crucial element in
efforts to constrain structure formation models, the normalisation of the
matter power spectrum and the cosmological matter density, and the nature and
evolution of dark energy. Large weak lensing surveys of ~20,000 galaxy clusters
and groups will be key tools in the observational pursuit of that goal. These
weak lensing studies often proceed by stacking the lensing signals of many
clusters and groups binned by mass-correlated observables such as richness and
luminosity; typically such analyses ignore the triaxial structure of dark
matter halos on the assumption that the averaging of many shear signals within
each mass bin makes its effects (as large as factors of two in mass model
parameter estimates from individual clusters) negligible. We test this
assumption and find that triaxiality can bias 3D virial mass estimates compared
to those for a spherical population by a few percent if suboptimal mass
estimators are used. This bias affects not only direct lensing constraints on
the mass function but can also affect the scatter and normalization of the
mass-observable relations derived from lensing that are so crucial to
constraining the cluster mass function with large samples. However, we
demonstrate that a careful choice of mass estimator can remove the bias very
effectively if the lensing signals from a sufficient number of triaxial halos
are averaged together, and further quantify that sufficient number for adequate
shape averaging. We thus show that by choosing observable bins to contain an
adequate number of halos and by utilizing a carefully chosen 3D mass estimator
stacked weak-lensing analyses can give unbiased constraints on the triaxial
mass function. |
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