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A multiwavelength study of the IRAS Deep Survey galaxy sample III.
Spectral classification and dynamical properties: The infrared deep sample (IDS), in the north ecliptical polar region (NEPR),
is the first complete, far--IR selected sample, on which numerous studies of
galaxy evolution are based. Here we present and analyze the spectral
classification of several galaxies in the IDS sample together with rotation
curves which allow estimating the lower mass limits of a subsample of objects.
We measured fluxes and intensity ratios of the emission lines in the visible
region of the spectrum (lambda 4000-9000 A) for 75 galaxy members. Moreover,
for some of them (55%), the spectra obtained with the Keck II telescope have
sufficient wavelength and spatial resolution to derive their rotation curve.
These galaxies turn out to be disk like systems, with a high fraction (~50%) of
interacting systems. The spectroscopic classification of 42 galaxies, using the
emission-line ratio diagnostic diagrams, shows that the NEPR sample is
predominantly composed of starburst galaxies (71%), while the fraction of AGNs
(7%) and LINERs (21%) is small. The dynamical analysis allows us to estimate
the lower mass limits of 39 galaxies. The rest-frame FIR luminosity
distribution of these galaxies spans the same range as that of the FIR selected
complete sample, i.e. three orders of magnitude, with the same mean value,
log(L_FIR)=10.2. This emphasizes that such galaxies represent FIR properties of
the whole sample well. Moreover, their optical properties are typical of the
sample itself since 62% of these belong to the 60mu selected complete sample. | The Cosmic Microwave Background and $H_0$: The cosmic microwave background (CMB) offers a unique window into the early
universe, providing insights into cosmological parameters like the Hubble
constant. Recent precise measurements of the CMB by experiments like Planck
seem to point to a lower value for the Hubble constant compared to some other
measurements like those from Type Ia supernovae. This discrepancy, known as the
Hubble tension, currently lacks a definitive explanation. In this chapter, we
provide an overview of how the Hubble constant is determined from detailed
measurements of the CMB power spectrum. We explain the physics underlying key
features of the CMB spectrum and their connection to cosmological parameters.
We then examine the consistency of Planck's Hubble constant determination, both
internally within the data itself and externally with other astrophysical
probes. While largely consistent, some anomalies like the lensing amplitude
parameter $A_L$ remain unresolved. We also explore various theoretical
extensions to the standard ${\Lambda}$CDM cosmological model and assess their
potential to resolve the Hubble tension. No clear resolution emerges,
indicating significant tensions remain between early and late universe probes
within simple extensions to ${\Lambda}$CDM. Upcoming CMB experiments promise
improved precision and should provide further insights into this cosmic
conundrum. A coherent picture bridging measurements across cosmic time remains
an open challenge at the forefront of modern cosmology. |
Gravitational Fragmentation in Galaxy Mergers: A Stability Criteria: We study the gravitational stability of gaseous streams in the complex
environment of a galaxy merger, because mergers are known to be places of
ongoing massive cluster formation and bursts of star formation. We find an
analytic stability parameter for case of gaseous streams orbiting around the
merger remnant. We test our stability criteria using hydrodynamical simulations
of galaxy mergers, obtaining satisfactory results. We find that our criteria
successfully predicts the streams that will be gravitationally unstable to
fragment into clumps. | Constraints on dark matter interactions with standard model particles
from CMB spectral distortions: We propose a new method to constrain elastic scattering between dark matter
(DM) and standard model particles in the early Universe. Direct or indirect
thermal coupling of non-relativistic DM with photons leads to a heat sink for
the latter. This results in spectral distortions of the cosmic microwave
background (CMB), the amplitude of which can be as large as a few times the
DM-to-photon number ratio. We compute CMB spectral distortions due to
DM-proton, DM-electron and DM-photon scattering for generic energy-dependent
cross sections and DM mass m_DM >~ 1 keV. Using FIRAS measurements we set
constraints on the cross sections for m_DM <~ 0.1 MeV. In particular, for
energy-independent scattering we obtain sigma[DM-proton] <~ 10^(-24) cm^2
(keV/m_DM)^(1/2), sigma[DM-electron] <~ 10^(-27) cm^2 (keV/m_DM)^(1/2) and
sigma[DM-photon] <~ 10^(-39) cm^2 (m_DM/keV). An experiment with the
characteristics of PIXIE would extend the regime of sensitivity up to masses
m_DM ~ 1 GeV. |
Beyond the Ultra-deep Frontier Fields And Legacy Observations (BUFFALO):
a high-resolution strong + weak-lensing view of Abell 370: The HST treasury program BUFFALO provides extended wide-field imaging of the
six Hubble Frontier Fields galaxy clusters. Here we present the combined strong
and weak-lensing analysis of Abell 370, a massive cluster at z=0.375. From the
reconstructed total projected mass distribution in the 6arcmin x 6arcmin
BUFFALO field-of-view, we obtain the distribution of massive substructures
outside the cluster core and report the presence of a total of seven
candidates, each with mass $\sim 5 \times 10^{13}M_{\odot}$. Combining the
total mass distribution derived from lensing with multi-wavelength data, we
evaluate the physical significance of each candidate substructure, and conclude
that 5 out of the 7 substructure candidates seem reliable, and that the mass
distribution in Abell 370 is extended along the North-West and South-East
directions. While this finding is in general agreement with previous studies,
our detailed spatial reconstruction provides new insights into the complex mass
distribution at large cluster-centric radius. We explore the impact of the
extended mass reconstruction on the model of the cluster core and in
particular, we attempt to physically explain the presence of an important
external shear component, necessary to obtain a low root-mean-square separation
between the model-predicted and observed positions of the multiple images in
the cluster core. The substructures can only account for up to half the
amplitude of the external shear, suggesting that more effort is needed to fully
replace it by more physically motivated mass components. We provide public
access to all the lensing data used as well as the different lens models. | The Correlated Formation Histories of Massive Galaxies and Their Dark
Matter Halos: Using observations in the COSMOS field, we report an intriguing correlation
between the star formation activity of massive (~10^{11.4}\msol) central
galaxies, their stellar masses, and the large-scale (~10 Mpc) environments of
their group-mass (~10^{13.6}\msol) dark matter halos. Probing the redshift
range z=[0.2,1.0], our measurements come from two independent sources: an X-ray
detected group catalog and constraints on the stellar-to-halo mass relation
derived from a combination of clustering and weak lensing statistics. At z=1,
we find that the stellar mass in star-forming centrals is a factor of two less
than in passive centrals at the same halo mass. This implies that the presence
or lack of star formation in group-scale centrals cannot be a stochastic
process. By z=0, the offset reverses, probably as a result of the different
growth rates of these objects. A similar but weaker trend is observed when
dividing the sample by morphology rather than star formation. Remarkably, we
find that star-forming centrals at z~1 live in groups that are significantly
more clustered on 10 Mpc scales than similar mass groups hosting passive
centrals. We discuss this signal in the context of halo assembly and recent
simulations, suggesting that star-forming centrals prefer halos with higher
angular momentum and/or formation histories with more recent growth; such halos
are known to evolve in denser large-scale environments. If confirmed, this
would be evidence of an early established link between the assembly history of
halos on large scales and the future properties of the galaxies that form
inside them. |
Scale-invariant helical magnetic field evolution and the duration of
inflation: We consider a scale-invariant helical magnetic field generated during
inflation. We show that, if the mean magnetic helicity density of such a field
is measured, it can be used to determine a lower bound on the duration of
inflation. Upper bounds can be used to derive constraints on the minimal
duration of inflation if one assumes that the magnetic field generated during
inflation is helical. Using three-dimensional simulations, we show that an
initially scale-invariant field develops, which is similar both with and
without magnetic helicity. In the fully helical case, however, the magnetic
field appears to have a more pronounced folded structure. | Modelling Time-varying Dark Energy with Constraints from Latest
Observations: We introduce a set of two-parameter models for the dark energy equation of
state (EOS) $w(z)$ to investigate time-varying dark energy. The models are
classified into two types according to their boundary behaviors at the redshift
$z=(0,\infty)$ and their local extremum properties. A joint analysis based on
four observations (SNe + BAO + CMB + $H_0$) is carried out to constrain all the
models. It is shown that all models get almost the same $\chi^2_{min}\simeq
469$ and the cosmological parameters $(\Omega_M, h, \Omega_bh^2)$ with the
best-fit results $(0.28, 0.70, 2.24)$, although the constraint results on two
parameters $(w_0, w_1)$ and the allowed regions for the EOS $w(z)$ are
sensitive to different models and a given extra model parameter. For three of
Type I models which have similar functional behaviors with the so-called CPL
model, the constrained two parameters $w_0$ and $w_1$ have negative correlation
and are compatible with the ones in CPL model, and the allowed regions of
$w(z)$ get a narrow node at $z\sim 0.2$. The best-fit results from the most
stringent constraints in Model Ia give $(w_0,w_1) = (-0.96^{+0.26}_{-0.21},
-0.12^{+0.61}_{-0.89})$ which may compare with the best-fit results $(w_0,w_1)
= (-0.97^{+0.22}_{-0.18}, -0.15^{+0.85}_{-1.33})$ in the CPL model. For four of
Type II models which have logarithmic function forms and an extremum point, the
allowed regions of $w(z)$ are found to be sensitive to different models and a
given extra parameter. It is interesting to obtain two models in which two
parameters $w_0$ and $w_1$ are strongly correlative and appropriately reduced
to one parameter by a linear relation $w_1 \propto (1+w_0)$. |
Quantitative Constraints on the Reionization History from the IGM
Damping Wing Signature in Two Quasars at z > 7: During reionization, neutral hydrogen in the intergalactic medium (IGM)
imprints a damping wing absorption feature on the spectrum of high-redshift
quasars. A detection of this signature provides compelling evidence for a
significantly neutral Universe, and enables measurements of the hydrogen
neutral fraction $x_{\rm HI}(z)$ at that epoch. Obtaining reliable quantitative
constraints from this technique, however, is challenging due to stochasticity
induced by the patchy inside-out topology of reionization, degeneracies with
quasar lifetime, and the unknown unabsorbed quasar spectrum close to rest-frame
Ly$\alpha$. We combine a large-volume semi-numerical simulation of reionization
topology with 1D radiative transfer through high-resolution hydrodynamical
simulations of the high-redshift Universe to construct models of quasar
transmission spectra during reionization. Our state-of-the-art approach
captures the distribution of damping wing strengths in biased quasar halos that
should have reionized earlier, as well as the erosion of neutral gas in the
quasar environment caused by its own ionizing radiation. Combining this
detailed model with our new technique for predicting the quasar continuum and
its associated uncertainty, we introduce a Bayesian statistical method to
jointly constrain the neutral fraction of the Universe and the quasar lifetime
from individual quasar spectra. We apply this methodology to the spectra of the
two highest redshift quasars known, ULAS J1120+0641 and ULAS J1342+0928, and
measured volume-averaged neutral fractions $\langle x_{\rm HI}
\rangle(z=7.09)=0.48^{+0.26}_{-0.26}$ and $\langle x_{\rm HI}
\rangle(z=7.54)=0.60^{+0.20}_{-0.23}$ (posterior medians and 68% credible
intervals) when marginalized over quasar lifetimes of $10^3 \leq t_{\rm q} \leq
10^8$ years. | The Formation History of the Ultra-Faint Dwarf Galaxies: We present early results from a Hubble Space Telescope survey of the
ultra-faint dwarf galaxies. These Milky Way satellites were discovered in the
Sloan Digital Sky Survey, and appear to be an extension of the classical dwarf
spheroidals to low luminosities, offering a new front in the efforts to
understand the missing satellite problem. Because they are the least luminous,
most dark matter dominated, and least chemically evolved galaxies known, the
ultra-faint dwarfs are the best candidate fossils from the early universe. The
primary goal of the survey is to measure the star-formation histories of these
galaxies and discern any synchronization due to the reionization of the
universe. We find that the six galaxies of our survey have very similar
star-formation histories, and that each is dominated by stars older than 12
Gyr. |
Navarro-Frenk-White dark matter profile and the dark halos around disk
systems: The $\Lambda$ cold dark matter ($\Lambda$CDM) scenario well describes the
Universe at large scales, but shows some serious difficulties at small scales:
the inner dark matter (DM) density profiles of spiral galaxies generally appear
to be cored, without the $r^{-1}$ predicted by N-body simulations in the above
scenario.
In a more physical context, the baryons in the galaxy might backreact and
erase the original cusp through supernova explosions. Before that this effect
be investigated, it is important to determine how wide and frequent the
discrepancy between observed and N-body predicted profiles is and what its
features are. We used more than 3200 quite extended rotation curves (RCs) of
good quality and high resolution of disk systems. The curves cover all
magnitude ranges. These RCs were condensed into 26 coadded RCs, each of them
built with individual RCs of galaxies of similar luminosity and morphology. We
performed mass models of these 26 RCs using the Navarro-Frenk-White (NFW)
profile for the contribution of the DM halo to the circular velocity and the
exponential Freeman disk for that of the stellar disk. The fits are generally
poor in all the 26 cases: in several cases, we find $\chi^2_{red}>2$. Moreover,
the best-fitting values of three parameters of the model ($c$, $M_D$, and
$M_{vir}$) combined with those of their 1$\sigma$ uncertainty clearly
contradict well-known expectations of the $\Lambda$CDM scenario. We also tested
the scaling relations that exist in spirals with the fitting outcome: the
modeling does not account for these scaling relations.
Therefore, NFW halo density law cannot account for the kinematics of the
whole family of disk galaxies. It is therefore mandatory for the $\Lambda CDM$
scenario in any disk galaxy of any luminosity to transform initial cusps into
the observed cores. | The effect of massive neutrinos on the BAO peak: We study the impact of neutrino masses on the shape and height of the BAO
peak of the matter correlation function, both in real and redshift space. In
order to describe the nonlinear evolution of the BAO peak we run N-body
simulations and compare them with simple analytic formulae. We show that the
evolution with redshift of the correlation function and its dependence on the
neutrino masses is well reproduced in a simplified version of the Zel'dovich
approximation, in which the mode-coupling contribution to the power spectrum is
neglected. While in linear theory the BAO peak decreases for increasing
neutrino masses, the effect of nonlinear structure formation goes in the
opposite direction, since the peak broadening by large scale flows is less
effective. As a result of this combined effect, the peak decreases by $\sim 0.6
\%$ for $ \sum m_\nu = 0.15$ eV and increases by $\sim1.2 \%$ for $ \sum m_\nu
= 0.3$ eV, with respect to a massless neutrino cosmology with equal value of
the other cosmological parameters. We extend our analysis to redshift space and
to halos, and confirm the agreement between simulations and the analytic
formulae. We argue that all analytical approaches having the Zel'dovich
propagator in their lowest order approximation should give comparable
performances, irrespectively to their formulation in Lagrangian or in Eulerian
space. |
ISiTGR: Testing deviations from GR at cosmological scales including
dynamical dark energy, massive neutrinos, functional or binned
parametrizations, and spatial curvature: We introduce a new version of the Integrated Software in Testing General
Relativity (ISiTGR) which is a patch to the software CAMB and CosmoMC. ISiTGR
is intended to test deviations from GR at cosmological scales using
cosmological data sets. While doing so, it allows for various extensions to the
standard flat $\Lambda$CDM model. In this new release, we have support for the
following: 1) dynamical dark energy parametrizations with a constant or
time-dependent equation of state; 2) a consistent implementation of anisotropic
shear to model massive neutrinos throughout the full formalism; 3) multiple
commonly-used parametrizations of modified growth (MG) parameters; 4)
functional, binned and hybrid time- and scale-dependencies for all MG
parameters; 5) spatially flat or curved backgrounds. ISiTGR is designed to
allow cosmological analyses to take full advantage of ongoing and future
surveys to test simultaneously or separately various extensions to the standard
model. We describe here the formalism and its implementation in the CMB code,
the Integrated Sachs-Wolfe (ISW) effect, and the 3x2 point statistics. Next, we
apply ISiTGR to current data sets from Planck-2018, Planck-2015, Dark Energy
Survey YR1 release, Baryonic Acoustic Oscillations (BAO), Redshift Space
Distortions (BAO/RSD) from the BOSS Data Release 12, the 6DF Galaxy Survey and
the SDSS Data Release 7 Main Galaxy Sample, and Supernova from the Pantheon
compilation, joint SNLS/SDSS data analysis and the Hubble Space Telescope. We
derive constraints on MG parameters for various combinations of the five
features above and find that GR is consistent with current data sets in all
cases. The code is made publicly available at
\url{https://github.com/mishakb/ISiTGR}. | Towards a model-independent reconstruction approach for late-time Hubble
data: Gaussian processes offers a convenient way to perform nonparametric
reconstructions of observational data assuming only a kernel which describes
the covariance between neighbouring points in a data set. We approach the
ambiguity in the choice of kernel in Gaussian processes with two methods -- (a)
approximate Bayesian computation with sequential Monte Carlo sampling and (b)
genetic algorithm -- and use the overall resulting method to reconstruct the
cosmic chronometers and supernovae type Ia data sets. The results have shown
that the Mat\'{e}rn$\left( \nu = 5/2 \right)$ kernel emerges on top of the
two-hyperparameter family of kernels for both cosmological data sets. On the
other hand, we use the genetic algorithm in order to select a most
naturally-fit kernel among a competitive pool made up of a ten-hyperparameters
class of kernels. Imposing a Bayesian information criterion-inspired measure of
the fitness, the results have shown that a hybrid of the Radial Basis Function
and the Mat\'{e}rn$\left( \nu = 5/2 \right)$ kernel best represented both data
sets. The kernel selection problem is not totally closed and may benefit from
further analysis using other strategies to resolve an optimal kernel for a
particular data set. |
Galaxy clusters as intrinsic alignment tracers: present and future: Galaxies and clusters embedded in the large-scale structure of the Universe
are observed to align in preferential directions. Galaxy alignment has been
established as a potential probe for cosmological information, but the
application of cluster alignments for these purposes remains unexplored.
Clusters are observed to have a higher alignment amplitude than galaxies, but
because galaxies are much more numerous, the trade-off in detectability between
the two signals remains unclear. We present forecasts comparing cluster and
galaxy alignments for two extragalactic survey set-ups: a currently-available
low redshift survey (SDSS) and an upcoming higher redshift survey (LSST). For
SDSS, we rely on the publicly available redMaPPer catalogue to describe the
cluster sample. For LSST, we perform estimations of the expected number counts
while we extrapolate the alignment measurements from SDSS. Clusters in SDSS
have typically higher alignment signal-to-noise than galaxies. For LSST, the
cluster alignment signals quickly wash out with redshift due to a relatively
low number count and a decreasing alignment amplitude. Nevertheless, a
potential strong-suit of clusters is in their interplay with weak lensing:
intrinsic alignments can be more easily isolated for clusters than for
galaxies. The signal-to-noise of cluster alignment can in general be improved
by isolating close pairs along the line of sight. | Evidence for a correlation between the sizes of quiescent galaxies and
local environment to z ~ 2: We present evidence for a strong relationship between galaxy size and
environment for the quiescent population in the redshift range 1 < z < 2.
Environments were measured using projected galaxy overdensities on a scale of
400 kpc, as determined from ~ 96,000 K-band selected galaxies from the UKIDSS
Ultra Deep Survey (UDS). Sizes were determined from ground-based K-band
imaging, calibrated using space-based CANDELS HST observations in the centre of
the UDS field, with photometric redshifts and stellar masses derived from
11-band photometric fitting. From the resulting size-mass relation, we confirm
that quiescent galaxies at a given stellar mass were typically ~ 50 % smaller
at z ~ 1.4 compared to the present day. At a given epoch, however, we find that
passive galaxies in denser environments are on average significantly larger at
a given stellar mass. The most massive quiescent galaxies (M_stellar > 2 x
10^11 M_sun) at z > 1 are typically 50 % larger in the highest density
environments compared to those in the lowest density environments. Using Monte
Carlo simulations, we reject the null hypothesis that the size-mass relation is
independent of environment at a significance > 4.8 sigma for the redshift range
1 < z < 2. In contrast, the evidence for a relationship between size and
environment is much weaker for star-forming galaxies. |
Cosmological Constraints on Higgs-Dilaton Inflation: We test the viability of the Higgs-dilaton model (HDM) compared to the
evolving dark energy ($w_0 w_a$CDM) model, in which the cosmological constant
model $\Lambda$CDM is also nested, by using the latest cosmological data that
includes the cosmic microwave background temperature, polarization and lensing
data from the \textit{Planck} satellite (2015 data release), the BICEP and Keck
Array experiments, the Type Ia supernovae from the JLA catalog, the baryon
acoustic oscillations from CMASS, LOWZ and 6dF, the weak lensing data from the
CFHTLenS survey and the matter power Spectrum measurements from the SDSS (data
release 7). We find that the values of all cosmological parameters allowed by
the Higgs-dilaton inflation model are well within the \textit{Planck} satellite
(2015 data release) constraints. In particular, we have that $w_0 =
-1.0001^{+0.0072}_{-0.0074}$, $w_a = 0.00^{+0.15}_{-0.16}$, $n_s =
0.9693^{+0.0083}_{-0.0082}$, $\alpha_s = -0.001^{+0.013}_{-0.014}$ and
$r_{0.05} = 0.0025^{+0.0017}_{-0.0016}$ (95.5\%C.L.). We also place new
stringent constraints on the couplings of the Higgs-dilaton model and we find
that $\xi_{\chi} < 0.00328$ and $\xi_h / \sqrt{\lambda} =
59200^{+30000}_{-20000}$ (95.5\%C.L.). Furthermore, we report that the HDM is
at a slightly better footing than the $w_0 w_a$CDM model, as they both have
practically the same chi-square, i.e. $\Delta \chi^2 = \chi^2_{w_0
w_a\mathrm{CDM}}-\chi^2_{\mathrm{HDM}}=0.18$, with the HDM model having two
fewer parameters. Finally Bayesian evidence favors equally the two models, with
the HDM being preferred by the AIC and DIC information criteria. | High Sensitivity Array Observations of the z=1.87 Sub-Millimeter Galaxy
GOODS 850-3: We present sensitive phase-referenced VLBI results on the radio continuum
emission from the z=1.87 luminous submillimeter galaxy (SMG) GOODS 850-3. The
observations were carried out at 1.4 GHz using the High Sensitivity Array
(HSA). Our sensitive tapered VLBI image of GOODS 850-3 at 0.47 x 0.34 arcsec
(3.9 x 2.9 kpc) resolution shows a marginally resolved continuum structure with
a peak flux density of 148 \pm 38 uJy/beam, and a total flux density of 168 \pm
73 uJy, consistent with previous VLA and MERLIN measurements. The derived
intrinsic brightness temperature is > 5 \pm 2 x 10^3 K. The radio continuum
position of this galaxy coincides with a bright and extended near-infrared
source that nearly disappears in the deep HST optical image, indicating a dusty
source of nearly 9 kpc in diameter. No continuum emission is detected at the
full VLBI resolution (13.2 x 7.2 mas, 111 x 61 pc), with a 4-sigma point source
upper limit of 26 uJy/beam, or an upper limit to the intrinsic brightness
temperature of 4.7 x 10^5 K. The extent of the observed continuum source at 1.4
GHz and the derived brightness temperature limits are consistent with the radio
emission (and thus presumably the far-infrared emission) being powered by a
major starburst in GOODS 850-3, with a star formation rate of ~2500 M_sun/yr.
Moreover, the absence of any continuum emission at the full resolution of the
VLBI observations indicates the lack of a compact radio AGN source in this
z=1.87 SMG. |
Cosmography and cosmic acceleration: We investigate the prospects for determining the accelerating history of the
Universe from upcoming measurements of the expansion rate $H(z)$. In our
analyses, we use Monte Carlo simulations based on $w$CDM models to generate
samples with different characteristics and calculate the evolution of the
deceleration parameter $q(z)$. We show that a cosmographic (and, therefore,
model-independent) evidence for cosmic acceleration ($q(z<z_t) < 0$, where
$z_t$ is the transition redshift) will only be possible with an accuracy in
$H(z)$ data greater than the expected in current planned surveys. A brief
discussion about the prospects for reconstructing the dark energy equation of
state from the parameters $H(z)$ and $q(z)$ is also included. | Lensing-induced morphology changes in CMB temperature maps in modified
gravity theories: Lensing of the Cosmic Microwave Background (CMB) changes the morphology of
pattern of temperature fluctuations, so topological descriptors such as
Minkowski Functionals can probe the gravity model responsible for the lensing.
We show how the recently introduced two-to-two and three-to-one kurt-spectra
(and their associated correlation functions), which depend on the power
spectrum of the lensing potential, can be used to probe modified gravity
theories such as $f({R})$ theories of gravity and quintessence models. We also
investigate models based on effective field theory, which include the
constant-$\Omega$ model, and low-energy Ho\vrava theories. Estimates of the
cumulative signal-to-noise for detection of lensing-induced morphology changes,
reaches ${\cal O}(10^3)$ for the future planned CMB polarization mission
COrE$^{+}$. Assuming foreground removal is possible to $\ell_{max}=3000$, we
show that many modified gravity theories can be rejected with a high level of
significance, making this technique comparable in power to galaxy weak lensing
or redshift surveys. These topological estimators are also useful in
distinguishing {\em lensing} from other scattering secondaries at the level of
the four-point function or trispectrum. Examples include the kinetic
Sunyaev-Zel'dovich (kSZ) effect which shares, with lensing, a lack of spectral
distortion. We also discuss the complication of foreground contamination from
unsubtracted point sources. |
Intrinsic galaxy shapes and alignments I: Measuring and modelling COSMOS
intrinsic galaxy ellipticities: The statistical properties of the ellipticities of galaxy images depend on
how galaxies form and evolve, and therefore constrain models of galaxy
morphology, which are key to the removal of the intrinsic alignment
contamination of cosmological weak lensing surveys, as well as to the
calibration of weak lensing shape measurements. We construct such models based
on the halo properties of the Millennium Simulation and confront them with a
sample of 90,000 galaxies from the COSMOS Survey, covering three decades in
luminosity and redshifts out to z=2. The ellipticity measurements are corrected
for effects of point spread function smearing, spurious image distortions, and
measurement noise. Dividing galaxies into early, late, and irregular types, we
find that early-type galaxies have up to a factor of two lower intrinsic
ellipticity dispersion than late-type galaxies. None of the samples shows
evidence for redshift evolution, while the ellipticity dispersion for late-type
galaxies scales strongly with absolute magnitude at the bright end. The
simulation-based models reproduce the main characteristics of the intrinsic
ellipticity distributions although which model fares best depends on the
selection criteria of the galaxy sample. We observe fewer close-to-circular
late-type galaxy images in COSMOS than expected for a sample of randomly
oriented circular thick disks and discuss possible explanations for this
deficit. | Void Lensing as a Test of Gravity: We investigate the potential of weak lensing by voids to test for deviations
from General Relativity. We calculate the expected lensing signal of a scalar
field with derivative couplings, finding that it has the potential to boost the
tangential shear both within and outside the void radius. We use voids traced
by Luminous Red Galaxies in SDSS to demonstrate the methodology of testing
these predictions. We find that the void central density parameter, as inferred
from the lensing signal, can shift from its GR value by up to 20% in some
galileon gravity models. Since this parameter can be estimated independently
using the galaxy tracer profiles of voids, our method provides a consistency
check of the gravity theory. Although galileon gravity is now disfavoured as a
source of cosmic acceleration by other datasets, the methods we demonstrate
here can be used to test for more general fifth force effects with upcoming
void lensing data. |
The Cosmological Effect of CMB/BAO Measurements: In this paper, the CMB/BAO measurements which cover the 13 redshift data in
the regime $0.106 \leq z \leq 2.34$ are given out. The CMB/BAO samples are
based on the BAO distance ratios $r_{s}(z_d)/D_{V}(z)$ and the CMB acoustic
scales $l_{A}$. It could give out the accelerating behaviors of the
$\Lambda$CDM, $w$CDM and o$\Lambda$CDM models. As the direction of the
degeneracy of $\Omega_{m0}-w$ and $\Omega_{m0}-\Omega_{k0}$ are different for
the CMB/BAO and BAO data, the CMB/BAO data show ability of breaking parameter
degeneracy. Our tightest constraining results is from the
BAO+Planck/BAO+$\Omega_{b}h^2$+$\Omega_{m}h^2$ data which has $\Omega_{m0}$
tension, but doesn't have $H_{0}$ tension with the Planck result. The extending
parameters $w$ and $\Omega_{k0}$ could alleviate the $\Omega_{m0}$ tensions
slightly. | Small-Scale Challenges to the $Λ$CDM Paradigm: The dark energy plus cold dark matter ($\Lambda$CDM) cosmological model has
been a demonstrably successful framework for predicting and explaining the
large-scale structure of Universe and its evolution with time. Yet on length
scales smaller than $\sim 1$ Mpc and mass scales smaller than $\sim 10^{11}
M_{\odot}$, the theory faces a number of challenges. For example, the observed
cores of many dark-matter dominated galaxies are both less dense and less cuspy
than naively predicted in $\Lambda$CDM. The number of small galaxies and dwarf
satellites in the Local Group is also far below the predicted count of low-mass
dark matter halos and subhalos within similar volumes. These issues underlie
the most well-documented problems with $\Lambda$CDM: Cusp/Core, Missing
Satellites, and Too-Big-to-Fail. The key question is whether a better
understanding of baryon physics, dark matter physics, or both will be required
to meet these challenges. Other anomalies, including the observed planar and
orbital configurations of Local Group satellites and the tight baryonic/dark
matter scaling relations obeyed by the galaxy population, have been less
thoroughly explored in the context of $\Lambda$CDM theory. Future surveys to
discover faint, distant dwarf galaxies and to precisely measure their masses
and density structure hold promising avenues for testing possible solutions to
the small-scale challenges going forward. Observational programs to constrain
or discover and characterize the number of truly dark low-mass halos are among
the most important, and achievable, goals in this field over then next decade.
These efforts will either further verify the $\Lambda$CDM paradigm or demand a
substantial revision in our understanding of the nature of dark matter. |
Improving Statistical Sensitivity of X-ray Searches for Axion-Like
Particles: X-ray observations of bright AGNs in or behind galaxy clusters offer unique
capabilities to constrain axion-like particles (ALPs). Existing analysis
technique rely on measurements of the global goodness-of-fit. We develop a new
analysis methodology that improves the statistical sensitivity to ALP-photon
oscillations by isolating the characteristic quasi-sinusoidal modulations
induced by ALPs. This involves analysing residuals in wavelength space allowing
the Fourier structure to be made manifest as well as a machine learning
approach. For telescopes with microcalorimeter resolution, simulations suggest
these methods give an additional factor of two in sensitivity to ALPs compared
to previous approaches. | Convolution Lagrangian perturbation theory for biased tracers beyond
general relativity: We compare analytic predictions for real and Fourier space two-point
statistics for biased tracers from a variety of Lagrangian Perturbation Theory
approaches against those from state of the art N-body simulations in $f(R)$
Hu-Sawicki and the nDGP braneworld modified gravity theories.
We show that the novel physics of gravitational collapse in scalar tensor
theories with the chameleon or the Vainshtein screening mechanism can be
effectively factored in with bias parameters analytically predicted using the
Peak-Background Split formalism when updated to include the environmental
sensitivity of modified gravity theories as well as changes to the halo mass
function.
We demonstrate that Convolution Lagrangian Perturbation Theory (CLPT) and
Standard Perturbation Theory (SPT) approaches provide accurate analytic methods
to predict the correlation function and power spectra, respectively, for biased
tracers in modified gravity models and are able to characterize both the BAO,
power-law and small scale regimes needed for upcoming galaxy surveys such as
DESI, Euclid, LSST and WFIRST. |
Complex particle acceleration processes in the hotspots of 3C105 and
3C445: We investigate the nature of the broad-band emission associated with the
low-power radio hotspots 3C105 South and 3C445 South. Both hotspot regions are
resolved in multiple radio/optical components. High-sensitivity radio VLA,
NIR/optical VLT and HST, and X-ray Chandra data have been used to construct the
multi-band spectra of individual hotspot components. The radio-to-optical
spectra of both hotspot regions are well fitted by a synchrotron model with
steep spectral indices ~0.8 and break frequencies 10^12-10^14 Hz. 3C105 South
is resolved in two optical components: a primary one, aligned with the jet
direction and possibly marking the first jet impact with the surrounding
medium, and a secondary, further out from the jet and extended in a direction
perpendicular to it. This secondary region is interpreted as a splatter-spot
formed by the deflection of relativistic plasma from the primary hotspot. Radio
and optical images of 3C445 South show a spectacular 10-kpc arc-shape structure
characterized by two main components, and perpendicular to the jet direction.
HST images in I and B bands further resolve the brightest components into thin
elongated features. In both 3C105 South and 3C445 South the main hotspot
components are enshrouded by diffuse optical emission on scale of several kpcs,
indicating that very high energy particles, possibly injected at strong shocks,
are continuously re-accelerated in situ by additional acceleration mechanisms.
We suggest that stochastic processes, linked to turbulence and instabilities,
could provide the required additional re-acceleration. | Density split statistics: joint model of counts and lensing in cells: We present density split statistics, a framework that studies lensing and
counts-in-cells as a function of foreground galaxy density, thereby providing a
large-scale measurement of both 2-point and 3-point statistics. Our method
extends our earlier work on trough lensing and is summarized as follows: given
a foreground (low redshift) population of galaxies, we divide the sky into
subareas of equal size but distinct galaxy density. We then measure lensing
around uniformly spaced points separately in each of these subareas, as well as
counts-in-cells statistics (CiC). The lensing signals trace the matter density
contrast around regions of fixed galaxy density. Through the CiC measurements
this can be related to the density profile around regions of fixed matter
density. Together, these measurements constitute a powerful probe of cosmology,
the skewness of the density field and the connection of galaxies and matter.
In this paper we show how to model both the density split lensing signal and
CiC from basic ingredients: a non-linear power spectrum, clustering hierarchy
coefficients from perturbation theory and a parametric model for galaxy bias
and shot-noise. Using N-body simulations, we demonstrate that this model is
sufficiently accurate for a cosmological analysis on year 1 data from the Dark
Energy Survey. |
The BEHOMO project: $Λ$LTB $N$-body simulations: Our Universe may feature large-scale inhomogeneities and anisotropies which
cannot be explained by the standard model of cosmology, that is, the
homogeneous and isotropic FLRW metric, on which the $\Lambda$CDM model is
built, may not describe accurately observations. Currently, there is not a
satisfactory understanding of the evolution of the large-scale structure on an
inhomogeneous background. We start the cosmology beyond homogeneity and
isotropy (BEHOMO) project and study the inhomogeneous $\Lambda$LTB model with
the methods of numerical cosmology. Understanding the evolution of the
large-scale structure is a necessary step to constrain inhomogeneous models
with present and future observables and place the standard model on more solid
grounds. We perform Newtonian $N$-body simulations, whose accuracy in
describing the background evolution is checked against the general relativistic
solution. The large-scale structure of the corresponding $\Lambda$CDM
simulation is also validated. We obtain the first set of simulations of the
$\Lambda$LTB model ever produced. The data products consist of 11 snapshots
between redshift 0 and 3.7 for each of the 68 simulations that have been
performed, together with halo catalogs and lens planes relative to 21
snapshots, between redshift 0 and 4.2, for a total of approximately 180 TB of
data. We plan to study the growth of perturbations at the linear and nonlinear
level, gravitational lensing, cluster abundances and proprieties. Data can be
obtained upon request. Further information is available at
valerio-marra.github.io/BEHOMO-project . | Status of QUBIC, the Q&U Bolometric Interferometer for Cosmology: The Q&U Bolometric Interferometer for Cosmology (QUBIC) is a novel kind of
polarimeter optimized for the measurement of the $B$-mode polarization of the
Cosmic Microwave Background (CMB), which is one of the major challenges of
observational cosmology. The signal is expected to be of the order of a few
tens of nK, prone to instrumental systematic effects and polluted by various
astrophysical foregrounds which can only be controlled through multichroic
observations. QUBIC is designed to address these observational issues with a
novel approach that combines the advantages of interferometry in terms of
control of instrumental systematics with those of bolometric detectors in terms
of wide-band, background-limited sensitivity. |
The strongest bounds on active-sterile neutrino mixing after Planck data: Light sterile neutrinos can be excited by oscillations with active neutrinos
in the early universe. Their properties can be constrained by their
contribution as extra-radiation, parameterized in terms of the effective number
of neutrino species N_ eff, and to the universe energy density today \Omega_\nu
h^2. Both these parameters have been measured to quite a good precision by the
Planck satellite experiment. We use this result to update the bounds on the
parameter space of (3+1) sterile neutrino scenarios, with an active-sterile
neutrino mass squared splitting in the range (10^{-5} - 10^2 ) eV^2. We
consider both normal and inverted mass orderings for the active and sterile
states. For the first time we take into account the possibility of two
non-vanishing active-sterile mixing angles. We find that the bounds are more
stringent than those obtained in laboratory experiments. This leads to a strong
tension with the short-baseline hints of light sterile neutrinos. In order to
relieve this disagreement, modifications of the standard cosmological scenario,
e.g. large primordial neutrino asymmetries, are required. | Cosmology with XMM galaxy clusters: the X-CLASS/GROND catalogue and
photometric redshifts: The XMM Cluster Archive Super Survey (X-CLASS) is a serendipitously-detected
X-ray-selected sample of 845 galaxy clusters based on 2774 XMM archival
observations and covering approximately 90 deg$^2$ spread across the
high-Galactic latitude ($|b|>20$ deg) sky. The primary goal of this survey is
to produce a well-selected sample of galaxy clusters on which cosmological
analyses can be performed. This article presents the photometric redshift
followup of a high signal-to-noise subset of 266 of these clusters with
declination $\delta<+20$ deg with GROND, a seven channel ($grizJHK$)
simultaneous imager on the MPG 2.2m telescope at the ESO La Silla Observatory.
We use a newly developed technique based on the red sequence colour-redshift
relation, enhanced with information coming from the X-ray detection to provide
photometric redshifts for this sample. We determine photometric redshifts for
236 clusters, finding a median redshift of $z=0.39$ with an accuracy of $\Delta
z = 0.02 (1+z)$ when compared to a sample of 76 spectroscopically confirmed
clusters. We also compute X-ray luminosities for the entire sample and find a
median bolometric luminosity of $7.2\times10^{43} \mathrm{erg\ s^{-1}}$ and a
median temperature 2.9 keV. We compare our results to the XMM-XCS and XMM-XXL
surveys, finding good agreement in both samples. The X-CLASS catalogue is
available online at http://xmm-lss.in2p3.fr:8080/l4sdb/. |
Synthetic simulations of the extragalactic sky seen by eROSITA. I.
Pre-launch selection functions from Monte-Carlo simulations: Studies of galaxy clusters provide stringent constraints on models of
structure formation. Provided that selection effects are under control, large
X-ray surveys are well suited to derive cosmological parameters, in particular
those governing the dark energy equation of state. We forecast the capabilities
of the all-sky eROSITA (the extended ROentgen Survey with an Imaging Telescope
Array) survey to be achieved by the early 2020s. We bring special attention to
modeling the entire chain from photon emission to source detection and
cataloguing. The selection function of galaxy clusters for the upcoming eROSITA
mission is investigated by means of extensive and dedicated Monte-Carlo
simulations. Employing a combination of accurate instrument characterization
and of state-of-the-art source detection technique, we determine a cluster
detection efficiency based on the cluster fluxes and sizes. Using this eROSITA
cluster selection function, we find that eROSITA will detect a total of $\sim
10^5$ clusters in the extra-galactic sky. This number of clusters will allow
eROSITA to put stringent constraints on cosmological models. We show that
incomplete assumptions on selection effects, such as neglecting the
distribution of cluster sizes, induce a bias in the derived value of
cosmological parameters. Synthetic simulations of the eROSITA sky capture the
essential characteristics impacting the next-generation galaxy cluster surveys
and they highlight parameters requiring tight monitoring in order to avoid
biases in cosmological analyses. | Pairwise Transverse Velocity Measurement with the Rees-Sciama Effect: We introduce a new estimator for the mean pairwise velocities of galaxy
clusters, which is based on the measurement of the clusters'
$\textit{transverse}$ velocity components. The Rees-Sciama (RS) effect offers
an opportunity to measure transverse peculiar velocities through its distinct
dipolar signature around the halo centers in the Cosmic Microwave Background
(CMB) temperature map. We exploit this dipolar structure to extract the
magnitude and direction of the transverse velocity vectors from CMB maps
simulated with the expected characteristics of future surveys like CMB-S4.
Although in the presence of lensed CMB and instrumental noise individual
velocities are not reliably reconstructed, we demonstrate that the mean
pairwise velocity measurement obtained using the estimator yields a
signal-to-noise ratio of $5.2$ for $\sim21,000$ halos with $M >
7\times10^{13}\rm M_\odot$ in a $40\times40$ [deg$^2$] patch at $z=0.5$. While
the proposed estimator carries promising prospects for measuring pairwise
velocities through the RS effect in CMB stage IV experiments, its applications
extend to any other potential probe of transverse velocities. |
Gas Emission Spectrum in the Irr Galaxy IC 10: Spectroscopic long-slit observations of the dwarf Irr galaxy IC 10 were
conducted at the 6-m Special Astrophysical Observatory telescope with the
SCORPIO focal reducer. The ionized-gas emission spectra in the regions of
intense current star formation were obtained for a large number of regions in
IC 10. The relative abundances of oxygen, N+, and S+ in about twenty HII
regions and in the synchrotron superbubble were estimated. We found that the
galaxy-averaged oxygen abundance is 12 + log(O/H) = 8.17 +- 0.35 and the
metallicity is Z = 0.18 +- 0.14 Z_sun. Our abundances estimated from the strong
emission lines are found to be more reliable than those obtained by comparing
diagnostic diagrams with photoionization models. | Growth of curvature perturbations for PBH formation \& detectable GWs in
non-minimal curvaton scenario revisited: We revisit the growth of curvature perturbations in non-minimal curvaton
scenario with a non-trivial field metric $\lambda(\phi)$ where $\phi$ is an
inflaton field, and incorporate the effect from the non-uniform onset of
curvaton's oscillation in terms of an axion-like potential. The field metric
$\lambda(\phi)$ plays a central role in the enhancement of curvaton field
perturbation $\delta\chi$, serving as an effective friction term which can be
either positive or negative, depending on the first derivative
$\lambda_{,\phi}$.Our analysis reveals that $\delta\chi$ undergoes the
superhorizon growth when the condition $\eta_\text{eff} \equiv - 2
\sqrt{2\epsilon} M_\text{Pl} { \lambda_{,\phi} \over \lambda} < -3$ is
satisfied. This is analogous to the mechanism responsible for the amplification
of curvature perturbations in the context of ultra-slow-roll inflation, namely
the growing modes dominate curvature perturbations. As a case study, we examine
the impact of a Gaussian dip in $\lambda(\phi)$ and conduct a thorough
investigation of both the analytical and numerical aspects of the inflationary
dynamics.Our findings indicate that the enhancement of curvaton perturbations
during inflation is not solely determined by the depth of the dip in
$\lambda(\phi)$. Rather, the first derivative $\lambda_{,\phi}$ also plays a
significant role, a feature that has not been previously highlighted in the
literature. Utilizing the $\delta \mathcal{N}$ formalism, we derive analytical
expressions for both the final curvature power spectrum and the non-linear
parameter $f_\text{NL}$ in terms of an axion-like curvaton's potential leading
to the non-uniform curvaton's oscillation. Additionally, the resulting
primordial black hole abundance and scalar-induced gravitational waves are
calculated, which provide observational windows for PBHs. |
Empirically-Driven Multiwavelength K-corrections At Low Redshift: K-corrections, conversions between flux in observed bands to flux in
rest-frame bands, are critical for comparing galaxies at various redshifts.
These corrections often rely on fits to empirical or theoretical spectral
energy distribution (SED) templates of galaxies. However, the templates limit
reliable K-corrections to regimes where SED models are robust. For instance,
the templates are not well-constrained in some bands (e.g., WISE W4), which
results in ill-determined K-corrections for these bands. We address this
shortcoming by developing an empirically-driven approach to K-corrections as a
means to mitigate dependence on SED templates. We perform a polynomial fit for
the K-correction as a function of a galaxy's rest-frame color determined in
well-constrained bands (e.g., rest-frame (g-r)) and redshift, exploiting the
fact that galaxy SEDs can be described as a one parameter family at low
redshift (0.01 < z < 0.09). For bands well-constrained by SED templates, our
empirically-driven K-corrections are comparable to the SED fitting method of
Kcorrect and SED template fitting employed in the GSWLC-M2 catalogue (the
updated medium-deep GALEX-SDSS-WISE Legacy Catalogue). However, our method
dramatically outperforms the available SED fitting K-corrections for WISE W4.
Our method also mitigates incorrect template assumptions and enforces the
K-correction to be 0 at z = 0. Our K-corrected photometry and code are publicly
available. | The Arecibo Legacy Fast ALFA Survey: VIII. HI Source Catalog of the
Anti-Virgo Region at dec = +25 deg: We present a fourth catalog of HI sources from the Arecibo Legacy Fast ALFA
(ALFALFA) Survey. We report 541 detections over 136 deg2, within the region of
the sky having 22h < R.A. < 03h and 24 deg < Dec. < 26 deg . This complements a
previous catalog in the region 26 deg < Dec. < 28 deg (Saintonge et al. 2008).
We present here the detections falling into three classes: (a) extragalactic
sources with S/N > 6.5, where the reliability of the catalog is better than
95%; (b) extragalactic sources 5.0 < S/N < 6.5 and a previously measured
optical redshift that corroborates our detection; or (c) High Velocity Clouds
(HVCs), or subcomponents of such clouds, in the periphery of the Milky Way. Of
the 541 objects presented here, 90 are associated with High Velocity Clouds,
while the remaining 451 are identified as extragalactic objects. Optical
counterparts have been matched with all but one of the extragalactic objects. |
Spatial density fluctuations and selection effects in galaxy redshift
surveys: One of the main problems of observational cosmology is to determine the range
in which a reliable measurement of galaxy correlations is possible. This
corresponds to determine the shape of the correlation function, its possible
evolution with redshift and the size and amplitude of large scale structures.
Different selection effects, inevitably entering in any observation, introduce
important constraints in the measurement of correlations. In the context of
galaxy redshift surveys selection effects can be caused by observational
techniques and strategies and by implicit assumptions used in the data
analysis. Generally all these effects are taken into account by using
pair-counting algorithms to measure two-point correlations. We review these
methods stressing that they are based on the a-priori assumption that galaxy
distribution is spatially homogeneous inside a given sample. We show that, when
this assumption is not satisfied by the data, results of the correlation
analysis are affected by finite size effects.In order to quantify these
effects, we introduce a new method based on the computation of the gradient of
galaxy counts along tiny cylinders. We show, by using artificial homogeneous
and inhomogeneous point distributions, that this method is to identify redshift
dependent selection effects and to disentangle them from the presence of large
scale density fluctuations. We then apply this new method to several redshift
catalogs and we find evidences that galaxy distribution, in those samples where
selection effects are small enough, is characterized by power-law correlations
with exponent $\gamma=0.9$ up to $20$ Mpc/h followed by a change of slope that,
in the range [20,100] Mpc/h, corresponds to a power-law exponent $\gamma=0.25$.
Whether a crossover to spatial unformity occurs at $\sim 100$ Mpc/h cannot be
clarified by the present data. | Systematics in Metallicity Gradient Measurements I : Angular Resolution,
Signal-to-Noise and Annuli Binning: With the rapid progress in metallicity gradient studies at high-redshift, it
is imperative that we thoroughly understand the systematics in these
measurements. This work investigates how the [NII]/Halpha ratio based
metallicity gradients change with angular resolution, signal-to-noise (S/N),
and annular binning parameters. Two approaches are used: 1. We downgrade the
high angular resolution integral-field data of a gravitationally lensed galaxy
and re-derive the metallicity gradients at different angular resolution; 2. We
simulate high-redshift integral field spectroscopy (IFS) observations under
different angular resolution and S/N conditions using a local galaxy with a
known gradient. We find that the measured metallicity gradient changes
systematically with angular resolution and annular binning. Seeing-limited
observations produce significantly flatter gradients than higher angular
resolution observations. There is a critical angular resolution limit beyond
which the measured metallicity gradient is substantially different to the
intrinsic gradient. This critical angular resolution depends on the intrinsic
gradient of the galaxy and is < 0.02 arcsec for our simulated galaxy. We show
that seeing-limited high-redshift metallicity gradients are likely to be
strongly affected by resolution-driven gradient flattening. Annular binning
with a small number of annuli produces a more flattened gradient than the
intrinsic gradient due to weak line smearing. For 3-annuli bins, a minimum S/N
of ~ 5 on the [NII] line is required for the faintest annulus to constrain the
gradients with meaningful errors. |
The elaboration of spiral galaxies: morpho-kinematics analyses of their
progenitors with IMAGES: The IMAGES project aims at measuring the velocity fields of a representative
sample of 100 massive galaxies at z=0.4-0.75, selected in the CDFS, the CFRS
and the HDFS fields. It uses the world-unique mode of multiple integral field
units of FLAMES/ GIRAFFE at VLT. The resolved-kinematics data allow us to
sample the large scale motions at ~ few kpc scale for each galaxy. They have
been combined with the deepest HST/ACS, Spitzer (MIPS and IRAC) and VLT/FORS2
ever achieved observations. Most intermediate redshift galaxies show anomalous
velocity fields: 6 Gyrs ago, half of the present day spirals were out of
equilibrium and had peculiar morphologies. The wealth of the data in these
fields allow us to modelize the physical processes in each galaxy with an
accuracy almost similar to what is done in the local Universe. These detailed
analyses reveal the importance of merger processes, including their remnant
phases. Together with the large evolution of spiral properties, this points out
the importance of disk survival and strengthens the disk rebuilding scenario.
This suggests that the hierarchical scenario may apply to the elaboration of
disk galaxies as it does for ellipticals. | The evolution of AGN across cosmic time: what is downsizing?: We use a coupled model of the formation and evolution of galaxies and black
holes (BH) to study the evolution of active galactic nuclei (AGN) in a cold
dark matter universe. The model predicts the BH mass, spin and mass accretion
history. BH mass grows via accretion triggered by discs becoming dynamically
unstable or galaxy mergers (called the starburst mode) and accretion from
quasi-hydrostatic hot gas haloes (called the hot-halo mode). By taking into
account AGN obscuration, we obtain a very good fit to the observed luminosity
functions (LF) of AGN (optical, soft and hard X-ray, and bolometric) for a wide
range of redshifts (0<z<6). The model predicts a hierarchical build up of BH
mass, with the typical mass of actively growing BHs increasing with decreasing
redshift. Remarkably, despite this, we find downsizing in the AGN population,
in terms of the differential growth with redshift of the space density of faint
and bright AGN. This arises naturally from the interplay between the starburst
and hot-halo accretion modes. The faint end of the LF is dominated by massive
BHs experiencing quiescent accretion via a thick disc, primarily during the
hot-halo mode. The bright end of the LF, on the other hand, is dominated by AGN
which host BHs accreting close to or in excess of the Eddington limit during
the starburst mode. The model predicts that the comoving space density of AGN
peaks at z~3, similar to the star formation history. However, when taking into
account obscuration, the space density of faint AGN peaks at lower redshift
(z<2) than that of bright AGN (z~2-3). This implies that the cosmic evolution
of AGN is shaped in part by obscuration. |
Can galaxy evolution mimic cosmic reionization?: Lyman-$\alpha$ (Ly$\alpha$) emitting galaxies are powerful tools to probe the
late stages of cosmic reionization. The observed sudden drop in Ly$\alpha$
fraction at $z>6$ is often interpreted as a sign of reionization, since the
intergalactic medium (IGM) is more neutral and opaque to Ly$\alpha$ photons.
Crucially, this interpretation of the observations is only valid under the
assumption that galaxies themselves experience a minimal evolution at these
epochs. By modelling Ly$\alpha$ radiative transfer effects in and around
galaxies, we examine whether a change in the galactic properties can reproduce
the observed drop in the Ly$\alpha$ fraction. We find that an increase in the
galactic neutral hydrogen content or a reduction in the outflow velocity toward
higher redshift both lead to a lower Ly$\alpha$ escape fraction, and can thus
mimic an increasing neutral fraction of the IGM. We furthermore find that this
change in galactic properties leads to systematically different Ly$\alpha$
spectra which can be used to differentiate the two competing effects. Using the
CANDELSz7 survey measurements which indicate slightly broader lines at $z\sim
6$, we find that the scenario of a mere increase in the galactic column density
towards higher $z$ is highly unlikely. We also show that a decrease in outflow
velocity is not ruled out by existing data but leads to more prominent blue
peaks at $z>6$. Our results caution the use of Ly$\alpha$ observations to
estimate the IGM neutral fraction without accounting for the potential change
in the galactic properties, e.g., by mapping out the evolution of Ly$\alpha$
spectral characteristics. | Quantifying the behaviour of curvature perturbations during inflation: How much does the curvature perturbation change after it leaves the horizon,
and when should one evaluate the power spectrum? To answer these questions we
study single field inflation models numerically, and compare the evolution of
different curvature perturbations from horizon crossing to the end of
inflation. In particular we calculate the number of efolds it takes for the
curvature perturbation at a given wavenumber to settle down to within a given
fraction of their value at the end of inflation. We find that e.g. in chaotic
inflation, the amplitude of the comoving and the curvature perturbation on
uniform density hypersurfaces differ by up to 180 % at horizon crossing
assuming the same amplitude at the end of inflation, and that it takes
approximately 3 efolds for the curvature perturbation to be within 1 % of its
value at the end of inflation. |
Gravitational Radiation from First-Order Phase Transitions: It is believed that first-order phase transitions at or around the GUT scale
will produce high-frequency gravitational radiation. This radiation is a
consequence of the collisions and coalescence of multiple bubbles during the
transition. We employ high-resolution lattice simulations to numerically evolve
a system of bubbles using only scalar fields, track the anisotropic stress
during the process and evolve the metric perturbations associated with
gravitational radiation. Although the radiation produced during the bubble
collisions has previously been estimated, we find that the coalescence phase
enhances this radiation even in the absence of a coupled fluid or turbulence.
We comment on how these simulations scale and propose that the same enhancement
should be found at the Electroweak scale; this modification should make direct
detection of a first-order electroweak phase transition easier. | CANDELS+3D-HST: compact SFGs at z~2-3, the progenitors of the first
quiescent galaxies: We analyze the star-forming and structural properties of 45 massive
(log(M/Msun)>10) compact star-forming galaxies (SFGs) at 2<z<3 to explore
whether they are progenitors of compact quiescent galaxies at z~2. The
optical/NIR and far-IR Spitzer/Herschel colors indicate that most compact SFGs
are heavily obscured. Nearly half (47%) host an X-ray bright AGN. In contrast,
only about 10% of other massive galaxies at that time host AGNs. Compact SFGs
have centrally-concentrated light profiles and spheroidal morphologies similar
to quiescent galaxies, and are thus strikingly different from other SFGs. Most
compact SFGs lie either within the SFR-M main sequence (65%) or below (30%), on
the expected evolutionary path towards quiescent galaxies. These results show
conclusively that galaxies become more compact before they lose their gas and
dust, quenching star formation. Using extensive HST photometry from CANDELS and
grism spectroscopy from the 3D-HST survey, we model their stellar populations
with either exponentially declining (tau) star formation histories (SFHs) or
physically-motivated SFHs drawn from semi-analytic models (SAMs). SAMs predict
longer formation timescales and older ages ~2 Gyr, which are nearly twice as
old as the estimates of the tau models. While both models yield good SED fits,
SAM SFHs better match the observed slope and zero point of the SFR-M main
sequence. Some low-mass compact SFGs (log(M/Msun)=10-10.6) have younger ages
but lower sSFRs than that of more massive galaxies, suggesting that the
low-mass galaxies reach the red sequence faster. If the progenitors of compact
SFGs are extended SFGs, state-of-the-art SAMs show that mergers and disk
instabilities are both able to shrink galaxies, but disk instabilities are more
frequent (60% versus 40%) and form more concentrated galaxies. We confirm this
result via high-resolution hydrodynamic simulations. |
Constraining Inflationary Scenarios with Braneworld Models and Second
Order Cosmological Perturbations: Inflationary cosmology is the leading explanation of the very early universe.
Many different models of inflation have been constructed which fit current
observational data. In this work theoretical and numerical methods for
constraining the parameter space of a wide class of such models are described.
First, string-theoretic models with large non-Gaussian signatures are
investigated. An upper bound is placed on the amplitude of primordial
gravitational waves produced by ultra-violet Dirac-Born-Infeld inflation. In
all but the most finely tuned cases, this bound is incompatible with a lower
bound derived for inflationary models which exhibit a red spectrum and
detectable non-Gaussianity. By analysing general non-canonical actions, a class
of models is found which can evade the upper bound when the phase speed of
perturbations is small. The multi-coincident brane scenario with a finite
number of branes is one such model. For models with a potentially observable
gravitational wave spectrum the number of coincident branes is shown to take
only small values. The second method of constraining inflationary models is the
numerical calculation of second order perturbations for a general class of
single field models. The Klein-Gordon equation at second order, written in
terms of scalar field variations only, is numerically solved. The slow roll
version of the second order source term is used and the method is shown to be
extendable to the full equation. This procedure allows the evolution of second
order perturbations in general and the calculation of the non-Gaussianity
parameter in cases where there is no analytical solution available. | Star-Forming Galaxies at z~2 in the Hubble Ultra Deep Field: Using a simple color selection based on B-, z- and K-band photometry, BzK=
(z-K)_AB-(B-z)_AB>-0.2, we picked out 52 star-forming galaxies at 1.4<z<2.5
(sBzKs) from a K-band selected sample (K_Vega<22.0) in an area of ~5.5 arcmin^2
of the Hubble Ultra Deep Field (UDF). We develop a new photometric redshift
method, and the error in our photometric redshifts is less than 0.02(1+z). From
the photometric redshift distribution, we find the BzK color criterion can be
used to select star-forming galaxies at 1.4<z<2.5 with K_Vega<22.0.
Down to K_Vega<22.0, the number counts of sBzKs increase linearly with the
K-band magnitude; the sBzKs are strongly clustered, and most of them have
irregular morphologies on the ACS images. They have a median reddening of
E(B-V)~0.28, an average star formation rate of ~36 M_sun/yr and a typical
stellar mass of 10^10 M_sun. The UV criterion for the galaxies at z~2 can
select most of the faint sBzKs in the UDF, but it does not work well for
bright, massive, highly-reddened, actively star-forming galaxies. |
Strongly Scale-dependent Non-Gaussianity: We discuss models of primordial density perturbations where the
non-Gaussianity is strongly scale-dependent. In particular, the non-Gaussianity
may have a sharp cut-off and be very suppressed on large cosmological scales,
but sizeable on small scales. This may have an impact on probes of
non-Gaussianity in the large-scale structure and in the cosmic microwave
background radiation anisotropies. | Alcock-Paczynski effects on wide-angle galaxy statistics: The Alcock-Paczynski (AP) effect is a geometrical distortion in
three-dimensional observed galaxy statistics. In anticipation of precision
cosmology based on ongoing and upcoming all-sky galaxy surveys, we build an
efficient method to compute the AP-distorted correlations of galaxy number
density and peculiar velocity fields for any larger angular scale not relying
on the conventionally used plane-parallel (PP) approximation. Here, instead of
the usual Legendre polynomial basis, the correlation functions are decomposed
using tripolar spherical harmonic basis; hence, characteristic angular
dependence due to the wide-angle AP effect can be rigorously captured. By means
of this, we demonstrate the computation of the AP-distorted correlations over
the various scales. Comparing our results with the PP-limit ones, we confirm
that the errors due to the PP approximation become more remarkable as the
visual angle of separation between target galaxies, $\Theta$, enlarges, and
especially for the density auto correlation, the error exceeds $10\%$ when
$\Theta \gtrsim 30^\circ$. This highlights the importance of the analysis
beyond the PP approximation. |
Testing Modified Gravity with Wide Binaries in GAIA DR2: Several recent studies have shown that very wide binary stars can potentially
provide an interesting test for modified-gravity theories which attempt to
emulate dark matter; these systems should be almost Newtonian according to
standard dark-matter theories, while the predictions for MOND-like theories are
distinctly different, if the various observational issues can be overcome. Here
we explore an observational application of the test from the recent GAIA DR2
data release: we select a large sample of $\sim 24,000$ candidate wide binary
stars with distance $< 200$ parsec and magnitudes $G < 16$ from GAIA DR2, and
estimated component masses using a main-sequence mass-luminosity relation. We
then compare the frequency distribution of pairwise relative projected velocity
(relative to circular-orbit value) as a function of projected separation; these
distributions show a clear peak at a value close to Newtonian expectations,
along with a long `tail' which extends to much larger velocity ratios; the
`tail' is considerably more numerous than in control samples constructed from
DR2 with randomised positions, so its origin is unclear. Comparing the velocity
histograms with simulated data, we conclude that MOND-like theories without an
external field effect are strongly inconsistent with the observed data since
they predict a peak-shift in clear disagreement with the data; testing
MOND-like theories with an external field effect is not decisive at present,
but has good prospects to become decisive in future with improved modelling or
understanding of the high-velocity tail, and additional spectroscopic data. | On the simulation of gravitational lensing: Gravitational lensing refers to the deflection of light by the gravity of
celestial bodies, often predominantly composed of dark matter. Seen through a
gravitational lens, the images of distant galaxies appear distorted. In this
paper we discuss simulation of the image distortion by gravitational lensing.
The objective is to enhance our understanding of how gravitational lensing
works through a simple tool to visualise hypotheses. The simulator can also
generate synthetic data for the purpose of machine learning, which will
hopefully allow us to invert the distortion function, something which is not
analytically possible at present. |
Bayesian hierarchical modelling of weak lensing - the golden goal: To accomplish correct Bayesian inference from weak lensing shear data
requires a complete statistical description of the data. The natural framework
to do this is a Bayesian Hierarchical Model, which divides the chain of
reasoning into component steps. Starting with a catalogue of shear estimates in
tomographic bins, we build a model that allows us to sample simultaneously from
the the underlying tomographic shear fields and the relevant power spectra
(E-mode, B-mode, and E-B, for auto- and cross-power spectra). The procedure
deals easily with masked data and intrinsic alignments. Using Gibbs sampling
and messenger fields, we show with simulated data that the large (over
67000-)dimensional parameter space can be efficiently sampled and the full
joint posterior probability density function for the parameters can feasibly be
obtained. The method correctly recovers the underlying shear fields and all of
the power spectra, including at levels well below the shot noise. | The surprising accuracy of isothermal Jeans modelling of
self-interacting dark matter density profiles: Recent claims of observational evidence for self-interacting dark matter
(SIDM) have relied on a semi-analytic method for predicting the density
profiles of galaxies and galaxy clusters containing SIDM. We present a thorough
description of this method, known as isothermal Jeans modelling, and then test
it with a large ensemble of haloes taken from cosmological simulations. Our
simulations were run with cold and collisionless dark matter (CDM) as well as
two different SIDM models, all with dark matter only variants as well as
versions including baryons and relevant galaxy formation physics. Using a mix
of different box sizes and resolutions, we study haloes with masses ranging
from 3e10 to 3e15 Msun. Overall, we find that the isothermal Jeans model
provides as accurate a description of simulated SIDM density profiles as the
Navarro-Frenk-White profile does of CDM halos. We can use the model
predictions, compared with the simulated density profiles, to determine the
input DM-DM scattering cross-sections used to run the simulations. This works
especially well for large cross-sections, while with CDM our results tend to
favour non-zero (albeit fairly small) cross-sections, driven by a bias against
small cross-sections inherent to our adopted method of sampling the model
parameter space. The model works across the whole halo mass range we study,
although including baryons leads to DM profiles of intermediate-mass (10^12 -
10^13 Msun) haloes that do not depend strongly on the SIDM cross-section. The
tightest constraints will therefore come from lower and higher mass haloes:
dwarf galaxies and galaxy clusters. |
Statistical mechanics of collisionless orbits. II. Structure of halos: In this paper, we present the density, \rho, velocity dispersion, \sigma, and
\rho/\sigma^3 profiles of isotropic systems which have the energy distribution,
N(E)\propto[\exp(\phi_0-E)-1], derived in Paper I. This distribution, dubbed
DARKexp, is the most probable final state of a collisionless self-gravitating
system, which is relaxed in terms of particle energies, but not necessarily in
terms of angular momentum. We compare the DARKexp predictions with the results
obtained using the extended secondary infall model (ESIM). The ESIM numerical
scheme is optimally suited for the purpose because (1) it relaxes only through
energy redistribution, leaving shell/particle angular momenta unaltered, and
(2) being a shell code with radially increasing shell thickness it has very
good mass resolution in the inner halo, where the various theoretical
treatments give different predictions. The ESIM halo properties, and especially
their energy distributions, are very well fit by DARKexp, implying that the
techniques of statistical mechanics can be used to explain the structure of
relaxed self-gravitating systems. | 13CO 1-0 imaging of the Medusa merger, NGC4194: Studying molecular gas properties in merging galaxies gives important clues
to the onset and evolution of interaction-triggered starbursts. The CO/13CO 1-0
line intensity ratio can be used as a tracer of how dynamics and star formation
processes impact the gas properties. The Medusa (NGC~4194) merger is
particularly interesting to study since its LFIR/LCO ratio rivals that of
ultraluminous galaxies (ULIRGs), despite the comparatively modest luminosity,
indicating an exceptionally high star formation efficiency (SFE) in the Medusa
merger.
Interferometric OVRO observations of CO and 13CO 1-0 in the Medusa show the
CO/13CO intensity ratio increases from normal, quiescent values (7-10) in the
outer parts (r>2 kpc) of the galaxy to high (16 to >40) values in the central
(r<1 kpc) starburst region. In the centre there is an east-west gradient where
the line ratio changes by more than a factor of three over 5" (945 pc). The
integrated 13CO emission peaks in the north-western starburst region while the
central CO emission is strongly associated with the prominent crossing
dust-lane. We discuss the central east-west gradient in the context of gas
properties in the starburst and the central dust lane. We suggest that the
central gradient is mainly caused by diffuse gas in the dust lane. In this
scenario, the actual molecular mass distribution is better traced by the 13CO
1-0 emission than the CO. The possibilities of temperature and abundance
gradients are also discussed. We compare the central gas properties of the
Medusa to those of other minor mergers and suggest that the extreme and
transient phase of the Medusa star formation activity has similar traits to
those of high-redshift galaxies. |
Submillimetre observations of galaxy clusters with BLAST: the
star-formation activity in Abell 3112: We present observations at 250, 350, and 500 um of the nearby galaxy cluster
Abell 3112 (z=0.075) carried out with BLAST, the Balloon-borne Large Aperture
Submillimeter Telescope. Five cluster members are individually detected as
bright submillimetre sources. Their far-infrared SEDs and optical colours
identify them as normal star-forming galaxies of high mass, with globally
evolved stellar populations. They all have B-R colours of 1.38+/-0.08,
transitional between the blue, active population and the red, evolved galaxies
that dominate the cluster core. We stack to determine the mean submillimetre
emission from all cluster members, which is determined to be 16.6+/-2.5,
6.1+/-1.9, and 1.5+/-1.3 mJy at 250, 350, and 500 um, respectively. Stacking
analyses of the submillimetre emission of cluster members reveal trends in the
mean far-infrared luminosity with respect to cluster-centric radius and Ks-band
magnitude. We find that a large fraction of submillimetre emission comes from
the boundary of the inner, virialized region of the cluster, at cluster-centric
distances around R_500. Stacking also shows that the bulk of the submillimetre
emission arises in intermediate-mass galaxies (L<L*), with Ks magnitude ~1 mag
fainter than the giant ellipticals. The results and constraints obtained in
this work will provide a useful reference for the forthcoming surveys to be
conducted on galaxy clusters by Herschel. | Constraining dark photons and their connection to 21 cm cosmology with
CMB data: In the inhomogeneous Universe, the cosmological conversion of dark photons
into ordinary photons (and vice versa) may happen at a great number of
resonance redshifts. This alters the CMB observed energy spectrum and degree of
small-scale anisotropies. We utilize results from the EAGLE simulation to
obtain the conversion probability along random line-of-sights to quantify these
effects. We then apply our results to the case where dark photons are sourced
by dark matter decay and their high-redshift conversion into ordinary photons
modify the global 21 cm signal expected from the cosmic dawn era. Concretely,
we show that a significant portion of the parameter space for which a converted
population of photons in the Rayleigh-Jeans tail of the CMB explains the
absorption strength observed by EDGES, is ruled out from the brightness
temperature measurements of COBE/FIRAS and the CMB anisotropy measurements of
Planck and SPT. |
Fractional Polarisation of Extragalactic Sources in the
500-square-degree SPTpol Survey: We study the polarisation properties of extragalactic sources at 95 and 150
GHz in the SPTpol 500 deg$^2$ survey. We estimate the polarised power by
stacking maps at known source positions, and correct for noise bias by
subtracting the mean polarised power at random positions in the maps. We show
that the method is unbiased using a set of simulated maps with similar noise
properties to the real SPTpol maps. We find a flux-weighted mean-squared
polarisation fraction $\langle p^2 \rangle= [8.9\pm1.1] \times 10^{-4}$ at 95
GHz and $[6.9\pm1.1] \times 10^{-4}$ at 150~GHz for the full sample. This is
consistent with the values obtained for a sub-sample of active galactic nuclei.
For dusty sources, we find 95 per cent upper limits of $\langle p^2
\rangle_{\rm 95}<16.9 \times 10^{-3}$ and $\langle p^2 \rangle_{\rm 150}<2.6
\times 10^{-3}$. We find no evidence that the polarisation fraction depends on
the source flux or observing frequency. The 1-$\sigma$ upper limit on measured
mean squared polarisation fraction at 150 GHz implies that extragalactic
foregrounds will be subdominant to the CMB E and B mode polarisation power
spectra out to at least $\ell\lesssim5700$ ($\ell\lesssim4700$) and
$\ell\lesssim5300$ ($\ell\lesssim3600$), respectively at 95 (150) GHz. | Under Einstein's Microscope: Measuring Properties of Individual Rotating
Massive Stars From Extragalactic Micro Caustic Crossings: Highly magnified stars residing in caustic crossing lensed galaxies at z ~
0.7-1.5 in galaxy cluster lensing fields inevitably exhibit recurrent
brightening events as they traverse a micro caustic network cast down by
foreground intracluster stars. The detectable ones belong to Nature's most
massive and luminous class of stars, with evolved blue supergiants being the
brightest ones at optical wavelengths. Considering single stars in this work,
we study to what extent intrinsic stellar parameters are measurable from
multi-filter lightcurves, which can be obtained with optical/near-IR space
telescopes during one or multiple caustic crossing events. We adopt a realistic
model for the axisymmetric surface brightness profiles of rotating O/B stars
and develop a numerical lensing code that treats finite-source-size effects.
With a single micro caustic crossing, the ratio of the surface rotation
velocity to the breakup value is measurable to an precision of ~ 0.1-0.2 for
feasible observation parameters with current space telescopes, with all unknown
intrinsic and extrinsic parameters marginalized over and without a degeneracy
with inclination. Equatorial radius and bolometric luminosity can be measured
to 1/3 and 2/3 of the fractional uncertainty in the micro caustic strength, for
which the value is not known at each crossing but an informative prior can be
obtained from theory. Parameter inference precision may be further improved if
multiple caustic crossing events for the same lensed star are jointly analyzed.
Our results imply new opportunities to survey individual massive stars in
star-formation sites at z ~ 0.7-1.5 or beyond. |
The BINGO Project I: Baryon Acoustic Oscillations from Integrated
Neutral Gas Observations: Observations of the redshifted 21-cm line of neutral hydrogen (HI) are a new
and powerful window of observation that offers us the possibility to map the
spatial distribution of cosmic HI and learn about cosmology. BINGO (Baryon
Acoustic Oscillations [BAO] from Integrated Neutral Gas Observations) is a new
unique radio telescope designed to be one of the first to probe BAO at radio
frequencies. BINGO has two science goals: cosmology and astrophysics. Cosmology
is the main science goal and the driver for BINGO's design and strategy. The
key of BINGO is to detect the low redshift BAO to put strong constraints in the
dark sector models. Given the versatility of the BINGO telescope, a secondary
goal is astrophysics, where BINGO can help discover and study Fast Radio Bursts
(FRB) and other transients, Galactic and extragalactic science. In this paper,
we introduce the latest progress of the BINGO project, its science goals,
describing the scientific potential of the project in each science and the new
developments obtained by the collaboration. We introduce the BINGO project and
its science goals and give a general summary of recent developments in
construction, science potential and pipeline development obtained by the BINGO
collaboration in the past few years. We show that BINGO will be able to obtain
competitive constraints for the dark sector, and also that will allow for the
discovery of several FRBs in the southern hemisphere. The capacity of BINGO in
obtaining information from 21-cm is also tested in the pipeline introduced
here. There is still no measurement of the BAO in radio, and studying cosmology
in this new window of observations is one of the most promising advances in the
field. The BINGO project is a radio telescope that has the goal to be one of
the first to perform this measurement and it is currently being built in the
northeast of Brazil. (Abridged) | Towards Accurate Modeling of Line-Intensity Mapping One-Point
Statistics: Including Extended Profiles: Line-intensity mapping (LIM) is quickly attracting attention as an
alternative technique to probe large-scale structure and galaxy formation and
evolution at high redshift. LIM one-point statistics are motivated because they
provide access to the highly non-Gaussian information present in line-intensity
maps and contribute to break degeneracies between cosmology and astrophysics.
Now that promising surveys are underway, an accurate model for the LIM
probability distribution function (PDF) is necessary to employ one-point
statistics. We consider the impact of extended emission and limited
experimental resolution in the LIM PDF for the first time. We find that these
effects result in a lower and broader peak at low intensities and a lower tail
towards high intensities. Focusing on the distribution of intensities in the
observed map, we perform the first model validation of LIM one-point statistics
with simulations and find good qualitative agreement. We also discuss the
impact on the covariance, and demonstrate that if not accounted for, large
biases in the astrophysical parameters can be expected in parameter inference.
These effects are also relevant for any summary statistic estimated from the
LIM PDF, and must be implemented to avoid biased results. The comparison with
simulations shows, however, that there are still deviations, mostly related
with the modeling of the clustering of emitters, which encourage further
development of the modeling of LIM one-point statistics. |
CONCERTO: Extracting the power spectrum of the [C II ] emission line: CONCERTO is the first experiment to perform a [CII] line intensity mapping
survey to target $z>5.2$. Measuring the [CII] power spectrum allows us to study
the role of dusty star-forming galaxies in the star formation history during
the Reionization and post-Reionization. The main obstacle to this measurement
is the contamination by bright foregrounds. We evaluate our ability to retrieve
the [CII] signal in mock observations using the Simulated Infrared Dusty
Extragalactic Sky. We compared two methods for dealing with the dust continuum
emission from galaxies: the standard PCA and the arPLS method. For line
interlopers, the strategy relies on masking low-redshift galaxies using
external catalogues. As we do not have observations of CO or classical CO
proxies ,we relied on the COSMOS stellar mass catalogue. To measure the power
spectrum of masked data, we adapted the P of K EstimatoR and discuss its use on
LIM data. The arPLS method achieves a reduction of the continuum background to
a sub-dominant level of the [CII] at z=7 by a factor of>70. When using PCA,
this factor is only 0.7. The masking lowers the power amplitude of line
contamination down to $2 \times 10^2 Jy^2/sr$ This residual level is dominated
by faint undetected sources. For our [CII] model, this results in a detection
at z = 5.2 with a power ratio [CII]/(residual interlopers) = $62 \pm 32$ for a
22 % area survey loss. However, at z = 7, [C II ] / (residual interlopers)$=2.0
\pm 1.4$. Thanks to the large area covered by SIDES-Uchuu, we show that the
power amplitude of line residuals varies by 12-15% for z=5.2-7. We present an
end-to-end simulation of the extragalactic foreground removal that we ran to
detect the [CII] at high redshift via its power spectrum. We show that dust
continuum emission are not a limiting foreground for [CII] LIM. Residual CO and
[CI] limits our ability to measure the [CII] power spectrum at z>7. | Effective Cross Section of Fuzzy Dark Matter Halos: We numerically study the movement of two colliding fuzzy dark matter solitons
without explicit self-interaction and find the effective cross section of
dissipative change in velocity. The cross section turns out to be inversely
proportional to the velocity cubed, and we present its analytic interpretation.
Using the result we roughly estimate spatial offsets during head-on collisions
of two fuzzy dark matter halos, which can be related to the spatial offsets
between stars and dark matter in collisions of some galaxy clusters. We also
show that the gravitational cooling plays an important role during the
collisions. |
Correlations of Dark Matter, Gas and Stellar Profiles in Dark Matter
Halos: Halos of similar mass and redshift exhibit a large degree of variability in
their differential properties, such as dark matter, hot gas, and stellar mass
density profiles. This variability is an indicator of diversity in the
formation history of these dark matter halos that is reflected in the coupling
of scatters about the mean relations. In this work, we show that the strength
of this coupling depends on the scale at which halo profiles are measured. By
analyzing the outputs of the IllustrisTNG hydrodynamical cosmological
simulations we report the radial- and mass-dependent couplings between the dark
matter, hot gas, and stellar mass radial density profiles utilizing the
population diversity in dark matter halos. We find that for the same mass halos
the scatters in the density of baryons and dark matter are strongly coupled at
large scales ($r>R_{200}$); but the coupling between gas and dark matter
density profiles fades near the core of halos ($r < 0.3 R_{200}$). We then show
that the correlation between halo profile and integrated quantities induces a
radius-dependent additive bias in the profile observables of halos when halos
are selected on properties other than their mass. We discuss the impact of this
effect on cluster abundance and cross-correlations cosmology with
multi-wavelength cosmological surveys. | The early early type: discovery of a passive galaxy at z=3: We present the discovery of a massive, quiescent galaxy at z=2.99. We have
obtained a HST/WFC3 spectrum of this object and measured its redshift from the
detection of a deep 4000A break consistent with an old population and a high
metallicity. By stellar population modeling of both its grism spectrum and
broad-band photometry, we derive an age of ~0.7 Gyr, implying a formation
redshift of z>4, and a mass >10^11 Msun. Although this passive galaxy is the
most distant confirmed so far, we find that it is slightly less compact than
other z>2 early-types of similar mass, being overall more analogous to those
z~1.6 field early-type galaxies. The discovery of this object shows that
early-type galaxies are detectable to at least z=3 and suggests that the
diversity of structural properties found in z=1.4-2 ellipticals to earlier
epochs could have its origin in a variety of formation histories among their
progenitors. |
Constraining f(R) theories with Type Ia Supernovae and Gamma Ray Bursts: Fourth - order gravity theories have received much interest in recent years
thanks to their ability to provide an accelerated cosmic expansion in a matter
only universe. In these theories, the Lagrangian density of the gravitational
field has the form R + f(R), and the explicit choice of the arbitrary function
f(R) must meet the local tests of gravity and the constraints from the
primordial abundance of the light elements. Two popular classes of f(R) models,
which are expected to fulfill all the above requirements, have recently been
proposed. However, neither of these models has ever been quantitatively tested
against the available astrophysical data. Here, by combining Type Ia Supernovae
and Gamma Ray Bursts, we investigate the ability of these models to reproduce
the observed Hubble diagram over the redshift range (0, 7). We find that both
models fit very well this dataset with the present day values of the matter
density and deceleration parameters which agree with previous estimates.
However, the strong degeneracy among the f(R) parameters prevents us from
putting strong constraints on the values of these parameters; nevertheless, we
can identify the regions of the parameter space that should, in principle, be
carefully explored with future data and dynamical probes in order to
discriminate among f(R) theories and standard dark energy models. | The Minimum Testable Abundance of Primordial Black Holes at Future
Gravitational-Wave Detectors: The next generation of gravitational-wave experiments, such as Einstein
Telescope, Cosmic Explorer and LISA, will test the primordial black hole
scenario. We provide a forecast for the minimum testable value of the abundance
of primordial black holes as a function of their masses for both the
unclustered and clustered spatial distributions at formation. In particular, we
show that these instruments may test abundances, relative to the dark matter,
as low as $10^{-10}$. |
Quasidecoupled state for dark matter in nonstandard thermal histories: Dark matter drops out of kinetic equilibrium with standard model particles
when the momentum-transfer rate equals the expansion rate. In a
radiation-dominated universe, this occurs at essentially the same time as dark
matter kinetically decouples from the plasma. Dark matter may also fall out of
kinetic equilibrium with standard model particles during an early
matter-dominated era (EMDE), which occurs when the energy content of the
Universe is dominated by either a decaying oscillating scalar field or a
semistable massive particle before big bang nucleosynthesis. Until now, it has
been assumed that kinetic decoupling during an EMDE happens similarly to the
way it does in a radiation-dominated era. We show that this is not the case. By
studying the evolution of the dark matter temperature, we establish a
quasidecoupled state for dark matter in an EMDE, during which the dark matter
temperature cools faster than the plasma temperature but slower than it would
cool if the dark matter were fully decoupled. The dark matter does not fully
decouple until the EMDE ends and the Universe becomes radiation dominated. We
also extend the criteria for quasidecoupling to other nonstandard thermal
histories and consider how quasidecoupling affects the free-streaming length of
dark matter. | Numerical modelling of the lobes of radio galaxies in cluster
environments: We have carried out two-dimensional, axisymmetric, hydrodynamic numerical
modelling of the evolution of radio galaxy lobes. The emphasis of our work is
on including realistic hot-gas environments in the simulations and on
establishing what properties of the resulting radio lobes are independent of
the choice of environmental properties and of other features of the models such
as the initial jet Mach number. The simulated jet power we use is chosen so
that we expect the inner parts of the lobes to come into pressure balance with
the external medium on large scales; we show that this leads to the expected
departure from self-similarity and the formation of characteristic central
structures in the hot external medium. The work done by the expanding radio
lobes on the external hot gas is roughly equal to the energy stored in the
lobes for all our simulations once the lobes are well established. We show that
the external pressure at the lobe midpoint is a reasonable estimate of the
internal (lobe) pressure, with only a weak dependence on the environmental
parameters: on the other hand, the predicted radio emission from a source of a
given physical size has a comparatively strong dependence on the environment in
which the lobe resides, introducing an order of magnitude of scatter into the
jet power versus radio luminosity relationship. X-ray surface brightness and
temperature visualizations of our simulations bear a striking resemblance to
observations of some well-studied radio galaxies. |
Gamma Ray Bursts as Probes of the Distant Universe: We review recent results on the high-redshift universe and the cosmic
evolution obtained using Gamma Ray Bursts (GRBs) as tracers of high-redshift
galaxies. Most of the results come from photometric and spectroscopic
observations of GRB host galaxies once the afterglow has faded away but also
from the analysis of the GRB afterglow line of sight as revealed by absorptions
in their optical spectrum. | Lensing covariance on cut sky and SPT-Planck lensing tensions: We investigate correlations induced by gravitational lensing on simulated
cosmic microwave background data of experiments with an incomplete sky coverage
and their effect on inferences from the South Pole Telescope data. These
correlations agree well with the theoretical expectations, given by the sum of
super-sample and intra-sample lensing terms, with only a typically negligible
$\sim$ 5% discrepancy in the amplitude of the super-sample lensing effect.
Including these effects we find that lensing constraints are in $3.0\sigma$ or
$2.1\sigma$ tension between the SPT polarization measurements and Planck
temperature or lensing reconstruction constraints respectively. If the
lensing-induced covariance effects are neglected, the significance of these
tensions increases to $3.5\sigma$ or $2.5\sigma$. Using the standard scaling
parameter $A_L$ substantially underestimates the significance of the tension
once other parameters are marginalized over. By parameterizing the super-sample
lensing through the mean convergence in the SPT footprint, we find a hint of
underdensity in the SPT region. We also constrain extra sharpening of the CMB
acoustic peaks due to missing smoothing of the peaks by super-sample lenses at
a level that is much smaller than the lens sample variance. Finally, we extend
the usual "shift in the means" statistic for evaluating tensions to
non-Gaussian posteriors, generalize an approach to extract correlation modes
from noisy simulated covariance matrices, and present a treatment of
correlation modes not as data covariances but as auxiliary model parameters. |
Structure and Substructure of Galactic Spheroids: The full spatio-chemo-dynamical structure of galaxies of all types and
environments at low redshift provides a critical accompaniment to observations
of galaxy formation at high redshift. The next decade brings the observational
opportunity to strongly constrain nearby galaxies' histories of star formation
and assembly, especially in the spheroids that comprise the large majority of
the stellar mass in the Universe but have until now been difficult to study. In
order to constrain the pathways to building up the spheroidal "red-sequence",
various standard techniques in photometry and spectroscopy, particularly with
resolved tracer populations like globular clusters and planetary nebulae, can
be scaled up to comprehensive surveys as improved wide-field instrumentation is
increasingly available. At the same time, progress in adaptive optics on giant
telescopes could for the first time permit deep, resolved photometric and
spectroscopic analysis of large samples of individual stars in these systems,
thereby revolutionizing galaxy studies. Strong theoretical support is needed in
order to understand the new observational constraints via detailed modeling and
self-consistent simulations of star and galaxy formation throughout cosmic
time. | Self-annihilating dark matter and the CMB: reionizing the Universe and
constraining cross sections: I summarize the recent advances in determining the effects of
self-annihilating WIMP dark matter on the modification of the recombination
history, at times earlier than the formation of astrophysical objects.
Depending on mass and self-annihilation cross section, WIMP DM can reproduce
sizable amounts of the total free electron abundance at z > 6; as known, this
affects the CMB temperature and polarization correlation spectra, and can be
used to place stringent bounds in the particle mass vs cross-section plane.
WMAP5 data already strongly disfavor the region capable to explain the recent
cosmic positron and electrons anomalies in terms of DM annihilation, whereas in
principle the Planck mission has the potential to see a signal produced by a
candidate laying in that region, or from WIMPs with thermal annihilation
cross-sections <sv>=3e-26 cm3/s and masses below 50 GeV. |
Agora: Multi-Component Simulation for Cross-Survey Science: The tightest cosmological constraints currently available are obtained by
combining complementary data sets. When combining correlated data sets, various
astrophysical biases that affect the measurements must be identified and
treated. There are numerous such biases, and they are often intricately related
with one another via complex astrophysical effects, making them difficult to
characterize analytically. Consequently, a simulation with multiple components
implemented coherently is required to investigate these biases simultaneously
and as a whole. In this work, a suite of simulated extragalactic skies is
presented, including maps and/or catalogues of cosmic microwave background
(CMB) lensing, thermal and kinetic Sunyaev-Zel'dovich (tSZ/kSZ) effects, cosmic
infrared background (CIB), radio sources, galaxy overdensity and galaxy weak
lensing. Each of these probes is implemented in the lightcone using halo
catalogues and/or particles from the Multidark-Planck2 (MDPL2) N-body
simulation, and the modelling is calibrated using hydrodynamic simulations and
publicly available data. The auto- and cross-spectra of the individual probes,
as well as the cross-spectra between the observables, are shown to be
consistent with theoretical models and measurements from data. The simulation
is shown to have a wide range of applications, including forecasting, pipeline
testing, and evaluating astrophysical biases in cross-correlation studies. It
is further demonstrated that the simulation products produced in this work have
sufficient accuracy to recover the input cosmology when subjected to a full
cosmological analysis and are ready for application in real-world analyses for
ongoing and future surveys. | Constraints on primordial black holes in the mixed dark matter scenarios
using the ratio $\rm (^3{He}+D)/H$: We derive the upper limit on the dark matter (DM) fraction in primordial
black holes (PBHs) in the mixed DM scenarios. In this scenarios, a PBH can
accrete weakly interacting massive particles (WIMPs) to form a ultracompact
minihalo (UCMH) with a density profile of $\rho_{\rm DM}(r)\sim r^{-9/4}$. The
energy released from UCMHs due to dark matter annihilation has influence on the
photodissociation of $^{4}{\rm He}$, producing the $^{3}{\rm He}$ and the D. By
requiring that the ratio $\rm (^3{He}+D)/H$ caused by UCMHs does not exceed the
measured value, we derive the upper limit on the dark matter fraction in PBHs.
For the canonical value of DM thermally averaged annihilation cross section
$\left<\sigma v\right>=3\times 10^{-26}\rm cm^{3}s^{-1}$, we find that the
upper limit is $f_{\rm PBH} < 0.35(0.75)$ for DM mass $m_{\chi}=1(10)~\rm GeV$.
Compared with other limits obtained by different astronomical measurements,
although our limit is not the strongest, we provide a different way of
constraining the cosmological abundance of PBHs. |
The Radio Signatures of the First Supernovae: Primordial stars are key to primeval structure formation as the first stellar
components of primeval galaxies, the sources of cosmic chemical enrichment and
likely cosmic reionization, and they possibly gave rise to the supermassive
black holes residing at the centres of galaxies today. While the direct
detection of individual Pop III stars will likely remain beyond reach for
decades to come, we show their supernova remnants may soon be detectable in the
radio. We calculate radio synchrotron signatures between 0.5 - 35 GHz from
hydrodynamical computations of the supernova remnants of Pop III stars in
minihaloes. We find that hypernovae yield the brightest systems, with observed
radio fluxes as high as 1 - 10 muJy. Less energetic Type II supernovae yield
remnants about a factor of 30 dimmer and pair-instability supernova remnants
are dimmer by a factor of more than 10,000. Because of the high gas densities
of the progenitor environments, synchrotron losses severely limit the maximum
emission frequencies, producing a distinctive peaked radio spectrum
distinguishable from normal galactic supernova remnant spectra. Hypernovae
radio remnants should be detectable by existing radio facilities like eVLA and
eMERLIN while Type II supernova remnants will require the Square Kilometre
Array. The number counts of hypernova remnants at z > 20 with fluxes above 1
muJy are expected to be one per hundred square degree field, increasing to a
few per square degree if they form down to z = 10. The detection of a z > 20
Type II supernova remnant brighter than 1 nJy would require a 100 - 200 square
degree field, although only a 1 - 2 square degree field for those forming down
to z = 10. Hypernova and Type II supernova remnants are easily separated from
one another by their light curves, which will enable future surveys to use them
to constrain the initial mass function of Pop III stars. | CMB Bispectrum from Primordial Scalar, Vector and Tensor
non-Gaussianities: We present an all-sky formalism for the Cosmic Microwave Background (CMB)
bispectrum induced by the primordial non-Gaussianities not only in scalar but
also in vector and tensor fluctuations. We find that the bispectrum can be
formed in an explicitly rationally invariant way by taking into account the
angular and polarization dependences of the vector and tensor modes. To
demonstrate this and present how to use our formalism, we consider a specific
example of the correlation between two scalars and a graviton as the source of
non-Gaussianity. As a result, we show that the CMB reduced bispectrum of the
intensity anisotropies is evaluated as a function of the multipole and the
coupling constant between two scalars and a graviton denoted by $g_{tss}$;
$|b_{\ell \ell \ell}| \sim \ell^{-4} \times 8 \times 10^{-18} |g_{tss}|$. By
estimating the signal-to-noise ratio, we find that the constraint as $|g_{tss}|
< 6$ will be expected from the PLANCK experiment. |
A Counterpart to the Radial Orbit Instability in Triaxial Stellar
Systems: Self-consistent solutions for triaxial mass models are highly non-unique. In
general, some of these solutions might be dynamically unstable, making them
inappropriate as descriptions of steady-state galaxies. Here we demonstrate for
the first time the existence in triaxial galaxy models of an instability
similar to the radial-orbit instability of spherical models. The instability
manifests itself when the number of box orbits, with predominantly radially
motions, is sufficiently large. N-body simulations verify that the evolution is
due neither to chaotic orbits nor to departures of the model from
self-consistency, but rather to a collective mode. The instability transforms
the triaxial model into a more prolate, but still triaxial, configuration.
Stable triaxial models are obtained when the mass contribution of radial orbits
is reduced. The implications of our results for the shapes of dark-matter halos
are discussed. | Clustering of Low-Redshift (z <= 2.2) Quasars from the Sloan Digital Sky
Survey: We present measurements of the quasar two-point correlation function,
\xi_{Q}, over the redshift range z=0.3-2.2 based upon data from the SDSS. Using
a homogeneous sample of 30,239 quasars with spectroscopic redshifts from the
DR5 Quasar Catalogue, our study represents the largest sample used for this
type of investigation to date. With this redshift range and an areal coverage
of approx 4,000 deg^2, we sample over 25 h^-3 Gpc^3 (comoving) assuming the
current LCDM cosmology. Over this redshift range, we find that the
redshift-space correlation function, xi(s), is adequately fit by a single
power-law, with s_{0}=5.95+/-0.45 h^-1 Mpc and \gamma_{s}=1.16+0.11-0.16 when
fit over s=1-25 h^-1 Mpc. Using the projected correlation function we calculate
the real-space correlation length, r_{0}=5.45+0.35-0.45 h^-1 Mpc and
\gamma=1.90+0.04-0.03, over scales of rp=1-130 h^-1 Mpc. Dividing the sample
into redshift slices, we find very little, if any, evidence for the evolution
of quasar clustering, with the redshift-space correlation length staying
roughly constant at s_{0} ~ 6-7 h^-1 Mpc at z<2.2 (and only increasing at
redshifts greater than this). Comparing our clustering measurements to those
reported for X-ray selected AGN at z=0.5-1, we find reasonable agreement in
some cases but significantly lower correlation lengths in others. We find that
the linear bias evolves from b~1.4 at z=0.5 to b~3 at z=2.2, with
b(z=1.27)=2.06+/-0.03 for the full sample. We compare our data to analytical
models and infer that quasars inhabit dark matter haloes of constant mass M ~2
x 10^12 h^-1 M_Sol from redshifts z~2.5 (the peak of quasar activity) to z~0.
[ABRIDGED] |
Discovery of the X-ray selected galaxy cluster XMMU J0338.8+0021 at z =
1.49 - Indications for a young system with a forming brightest galaxy: We report on the discovery of a galaxy cluster at z = 1.490 originally
selected as an extended X-ray source in the XMM-Newton Distant Cluster Project.
Further observations carried out with the VLT-FORS2 spectrograph allowed the
spectroscopic confirmation of seven secure cluster members, providing a median
system redshift of z = 1.490 +/- 0.009. The color magnitude diagram of XMMU
J0338.8+0021 reveals the presence of a well populated red sequence with z-H ~
3, albeit with an apparent significant scatter in color. Since we do not detect
indications for strong star formation activity in any of the objects, the color
spread could indicate different stellar ages of the member galaxies. In
addition, we found the brightest cluster galaxy in a very active dynamical
state, with an interacting, merging companion located at a physical projected
distance of d ~ 20kpc. From the X-ray luminosity we estimate a cluster mass of
M200 ~ 1.2 x 10^(14) Msun. The data seem to suggest a scenario in which XMMU
J0338.8+0021 is a young system, possibly caught in a moment of active ongoing
mass assembly. | Impact of Anisotropic Birefringence on Measuring Cosmic Microwave
Background Lensing: The power spectrum of cosmic microwave background lensing is a powerful tool
for constraining fundamental physics such as the sum of neutrino masses and the
dark energy equation of state. Current lensing measurements primarily come from
distortions to the microwave background temperature field, but the polarization
lensing signal will dominate upcoming experiments with greater sensitivity.
Cosmic birefringence refers to the rotation of the linear polarization
direction of microwave photons propagating from the last scattering surface to
us, which can be induced by parity-violating physics such as axion-like dark
matter or primordial magnetic fields. We find that, for an upcoming CMB-S4-like
experiment, if there exists the scale-invariant anisotropic birefringence with
an amplitude corresponding to the current $95\%$ upper bound, the measured
lensing power spectrum could be biased by up to a factor of few at small
scales, $L\gtrsim 1000$. We show that the bias scales linearly with the
amplitude of the scale-invariant birefringence spectrum. The signal-to-noise of
the contribution from anisotropic birefringence is larger than unity even if
the birefringence amplitude decreases to $\sim 5\%$ of the current upper bound.
Our results indicate that a measurement and characterization of the anisotropic
birefringence is important for lensing analysis in future low-noise
polarization experiments. |
Cross-correlation of DES Y3 lensing and ACT/${\it Planck}$ thermal
Sunyaev Zel'dovich Effect II: Modeling and constraints on halo pressure
profiles: Hot, ionized gas leaves an imprint on the cosmic microwave background via the
thermal Sunyaev Zel'dovich (tSZ) effect. The cross-correlation of gravitational
lensing (which traces the projected mass) with the tSZ effect (which traces the
projected gas pressure) is a powerful probe of the thermal state of ionized
baryons throughout the Universe, and is sensitive to effects such as baryonic
feedback. In a companion paper (Gatti et al. 2021), we present tomographic
measurements and validation tests of the cross-correlation between galaxy shear
measurements from the first three years of observations of the Dark Energy
Survey, and tSZ measurements from a combination of Atacama Cosmology Telescope
and ${\it Planck}$ observations. In this work, we use the same measurements to
constrain models for the pressure profiles of halos across a wide range of halo
mass and redshift. We find evidence for reduced pressure in low mass halos,
consistent with predictions for the effects of feedback from active galactic
nuclei. We infer the hydrostatic mass bias ($B \equiv M_{500c}/M_{\rm SZ}$)
from our measurements, finding $B = 1.8\pm0.1$ when adopting the ${\it
Planck}$-preferred cosmological parameters. We additionally find that our
measurements are consistent with a non-zero redshift evolution of $B$, with the
correct sign and sufficient magnitude to explain the mass bias necessary to
reconcile cluster count measurements with the ${\it Planck}$-preferred
cosmology. Our analysis introduces a model for the impact of intrinsic
alignments (IA) of galaxy shapes on the shear-tSZ correlation. We show that IA
can have a significant impact on these correlations at current noise levels. | Exploring Interacting Dark Energy with Chaos Quantum-Behaved Particle
Swarm Optimization: Models with an interaction between dark energy and dark matter have already
been studied for about twenty years. However, in this paper, we provide for the
first time a general analytical solution for models with an energy transfer
given by $\mathcal{E} = 3H(\xi_1 \rho_c + \xi_2 \rho_d)$. We also use a new set
of age-redshift data for 114 old astrophysical objects (OAO) and constrain some
special cases of this general energy transfer. We use a method inspired on
artificial intelligence, known as Chaos Quantum-behaved Particle Swarm
Optimization (CQPSO), to explore the parameter space and search the best fit
values. We test this method under a simulated scenario and also compare with
previous MCMC results and find good agreement with the expected results. |
Binary Black Holes, Gas Sloshing, and Cold Fronts in the X-ray Halo
Hosting 4C+37.11: We analyzed deep $Chandra$ ACIS-I exposures of the cluster-scale X-ray halo
surrounding the radio source 4C+37.11. This remarkable system hosts the closest
resolved pair of super-massive black hole and an exceptionally luminous
elliptical galaxy, the likely product of a series of past mergers. We
characterize the halo with $r_{500} = 0.95$ Mpc, $M_{500} = (2.5 \pm 0.2)
\times 10^{14} \ M_{\rm{\odot}}$, $ kT = 4.6\pm 0.2$ keV, and a gas mass of
$M_{\rm g,500} = (2.2 \pm 0.1) \times 10^{13} M_\odot$. The gas mass fraction
within $r_{500}$ is $f_{\rm g} = 0.09 \pm 0.01$. The entropy profile shows
large non-gravitational heating in the central regions. We see several surface
brightness jumps, associated with substantial temperature and density changes,
but approximate pressure equilibrium, implying that these are sloshing
structures driven by a recent merger. A residual intensity image shows core
spiral structure closely matching that seen for the Perseus cluster, although
at $z=0.055$ the spiral pattern is less distinct. We infer the most recent
merger occurred $1-2$ Gyr ago and that the event that brought the two observed
super-massive black holes to the system core is even older. Under that
interpretation, this black hole binary pair has, unusually, remained at
pc-scale separation for more than 2 Gyr. | First stars in Damped Lyman Alpha systems: In order to characterize Damped Lyman Alpha systems (DLAs) potentially
hosting first stars, we present a novel approach to investigate DLAs in the
context of Milky Way (MW) formation, along with their connection with the most
metal-poor stars and local dwarf spheroidal (dSph) galaxies. The merger tree
method previously developed is extended to include inhomogeneous reionization
and metal mixing, and it is validated by matching both the Metallicity
Distribution Function of Galactic halo stars and the Fe-Luminosity relation of
dSph galaxies. The model explains the observed NHI-Fe relation of DLAs along
with the chemical abundances of [Fe/H] < -2 systems. In this picture, the
recently discovered z_abs ~ 2.34 C-enhanced DLA (Cooke et al. 2011a), pertains
to a new class of absorbers hosting first stars along with second-generation
long-living low-mass stars. These "PopIII DLAs" are the descendants of
H2-cooling minihalos with Mh ~ 10^7 Msun, that virialize at z > 8 in neutral,
primordial regions of the MW environment and passively evolve after a short
initial period of star formation. The gas in these systems is warm Tg \sim
(40-1000) K, and strongly C-enriched by long-living, extremely metal-poor stars
of total mass M* \sim 10^{2-4} Msun. |
Accessing the Acceleration of the Universe with Sunyaev-Zel'dovich and
X-ray Data from Galaxy Clusters: By using exclusively the Sunyaev-Zel'dovich effect and X-ray surface
brightness data from 25 galaxy clusters in the redshift range 0.023< z < 0.784
we access cosmic acceleration employing a kinematic description. Such result is
fully independent on the validity of any metric gravity theory, the possible
matter-energy contents filling the Universe, as well as on the SNe Ia Hubble
diagram. | Constraining the Expansion History and Early Dark Energy with Line
Intensity Mapping: We consider the potential for line intensity mapping (IM) experiments to
measure the baryon acoustic oscillations (BAO) from 3 < z < 6. This would
constrain the expansion history in a redshift range that is currently
unexplored. We calculate the map depths that future IM experiments targeting
the CO(1-0) rotational transition line and [CII] ionized carbon fine-structure
line would need to achieve in order to measure the BAO. We find that
near-future IM experiments could constrain the BAO scale to 5% or better
depending on CO/[CII] model amplitude. This measurement is at a precision that
could make competitive constraints on models of early dark energy. |
Modelling the relative velocities of isolated pairs of galaxies: We study the comoving relative velocities, v12, of model isolated galaxy
pairs at z=0.5. For this purpose, we use the predictions from the GALFORM
semi-analytical model of galaxy formation and evolution based on a Lambda cold
dark matter cosmology consistent with the results from WMAP7. In real space, we
find that isolated pairs of galaxies are predicted to form an angle t with the
line-of-sight that is uniformily distributed as expected if the Universe is
homogeneous and isotropic. We also find that isolated pairs of galaxies
separated by a comoving distance between 1 and 3 Mpc/h are predicted to have
<v12>=0. For galaxies in this regime, the distribution of the angle t is
predicted to change minimally from real to redshift space, with a change
smaller than 5% in <sin^2 t>. However, the distances defining the comoving
regime strongly depends on the applied isolation criteria. | Observational Scan Induced Artificial CMB Anisotropy: To reliably detect the cosmic microwave background (CMB) anisotropy is of
great importance in understanding the birth and evolution of the Universe. One
of the difficulties in CMB experiments is the domination of measured CMB
anisotropy maps by the Doppler dipole moment from the motion of the antenna
relative to the CMB. For each measured temperature the expected dipole
component has to be calculated separately and then subtracted from the data. A
small error in dipole direction, antenna pointing direction, sidelobe pickup
contamination, and/or timing synchronism, can raise significant deviation in
the dipole cleaned CMB temperature. After a full-sky observational scan, the
accumulated deviations will be structured with a pattern closely correlated to
the observation pattern with artificial anisotropies on large scales, including
artificial quadrupole, octopole etc in the final CMB map. Such scan-induced
anisotropies on large scales can be predicted by the true dipole moment and
observational scan scheme. Indeed, the expected scan-induced quadrupole pattern
of the WMAP mission is perfectly in agreement with the published WMAP
quadrupole. With the scan strategy of the Planck mission, we predict that
scan-induced anisotropies will also produce an artificially aligned quadrupole.
The scan-induced anisotropy is a common problem for all sweep missions and,
like the foreground emissions, has to be removed from observed maps. Without
doing so, CMB maps from COBE, WMAP, and Planck as well, are not reliable for
studying the CMB anisotropy. |
Dipole Distortions in the Intergalactic Medium: Baryonic feedback can significantly modify the spatial distribution of matter
on small scales and create a bulk relative velocity between the dominant cold
dark matter and the hot gas. We study the consequences of such bulk motions
using two high resolution hydrodynamic simulations, one with no feedback and
one with very strong feedback. We find that relative velocities of order $100\
\kms$ are produced in the strong feedback simulation whereas it is much smaller
when there is no feedback. Such relative motions induce dipole distortions to
the gas, which we quantify by computing the dipole correlation function. We
find halo coordinates and velocities are systematically changed in the
direction of the relative velocity. Finally, we discuss potential to observe
the relative velocity via large scale structure, Sunyaev-Zel'dovich and line
emission measurements. Given the nonlinear nature of this effect, it should
next be studied in simulations with different feedback
implementations/strengths to determine the available model space. | Polycyclic Aromatic Hydrocarbons in Galaxies at z~0.1: the Effect of
Star Formation and AGN: We present the analysis of the Polycyclic Aromatic Hydrocarbon (PAH) spectra
of a sample of 92 typical star forming galaxies at 0.03 < z < 0.2 observed with
the Spitzer IRS. We compare the relative strengths of PAH emission features
with SDSS optical diagnostics to probe the relationship between PAH grain
properties and star formation and AGN activity. Short-to-long wavelength PAH
ratios, and in particular the 7.7-to-11.3 micron feature ratio, are strongly
correlated with the star formation diagnostics D_n(4000) and H-alpha equivalent
width, increasing with younger stellar populations. This ratio also shows a
significant difference between active and non-active galaxies, with the active
galaxies exhibiting weaker 7.7 micron emission. A hard radiation field as
measured by [OIII]/H-beta and [NeIII]_15.6/[NeII]_12.8 affects PAH ratios
differently depending on whether this field results from starburst activity or
an AGN. Our results are consistent with a picture in which larger PAH molecules
grow more efficiently in richer media and in which smaller PAH molecules are
preferentially destroyed by AGN. |
Mock data sets for the Eboss and DESI Lyman-$α$ forest surveys: {We present a publicly-available code to generate mock Lyman-$\alpha$ (\lya)
forest data sets. The code is based on the Fluctuating Gunn-Peterson
Approximation (FGPA) applied to Gaussian random fields and on the use of fast
Fourier transforms (FFT). The output includes spectra of lya transmitted flux
fraction, $F$, a quasar catalog, and a catalog of high-column-density systems.
While these three elements have realistic correlations, additional code is then
used to generate realistic quasar spectra, to add absorption by
high-column-density systems and metals, and to simulate instrumental effects.
Redshift space distortions (RSD) are implemented by including the large-scale
velocity-gradient field in the FGPA resulting in a correlation function of $F$
that can be accurately predicted. One hundred realizations have been produced
over the 14,000 deg$^2$ Dark Energy Spectroscopy Instrument (DESI) survey
footprint with 100 quasars per deg$^{2}$, and they are being used for the
Extended Baryon Oscillation Survey (eBOSS) and DESI surveys. The analysis of
these realizations shows that the correlation of $F$ follows the prediction
within the accuracy of eBOSS survey. The most time-consuming part of the
production occurs before application of the FGPA, and the existing pre-FGPA
forests can be used to easily produce new mock sets with modified
redshift-dependent bias parameters or observational conditions. | Joint Measurement of Lensing-Galaxy Correlations Using SPT and DES SV
Data: We measure the correlation of galaxy lensing and cosmic microwave background
lensing with a set of galaxies expected to trace the matter density field. The
measurements are performed using pre-survey Dark Energy Survey (DES) Science
Verification optical imaging data and millimeter-wave data from the 2500 square
degree South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey. The two
lensing-galaxy correlations are jointly fit to extract constraints on
cosmological parameters, constraints on the redshift distribution of the lens
galaxies, and constraints on the absolute shear calibration of DES galaxy
lensing measurements. We show that an attractive feature of these fits is that
they are fairly insensitive to the clustering bias of the galaxies used as
matter tracers. The measurement presented in this work confirms that DES and
SPT data are consistent with each other and with the currently favored
$\Lambda$CDM cosmological model. It also demonstrates that joint lensing-galaxy
correlation measurement considered here contains a wealth of information that
can be extracted using current and future surveys. |
The specific frequencies of ultra-compact dwarf galaxies: We aim at quantifying the specific frequency of UCDs in a range of
environments and at relating this to the frequency of globular clusters (GCs)
and potential progenitor dwarf galaxies. Are the frequencies of UCDs consistent
with being the bright tail of the GC luminosity function (GCLF)? We propose a
definition for the specific frequency of UCDs,
S_{N,UCD}=N_{UCD}*10^{0.4*(M_{V,host}-M_{V,0})}*c_{w}. The parameter M_{V,0} is
the zeropoint of the definition, chosen such that the specific frequency of
UCDs is the same as those of globular clusters, S_{N,GC}, if UCDs follow a
simple extrapolation of the GCLF. The parameter c_{w} is a correction term for
the GCLF width sigma. We apply our definition of S_{N,UCD} to results of
spectroscopic UCD searches in the Fornax, Hydra and Centaurus galaxy clusters,
two Hickson Compact Groups, and the Local Group. This includes a large database
of 180 confirmed UCDs in Fornax. We find that the specific frequencies derived
for UCDs match those of GCs very well, to within 10-50%. The ratio
{S_{N,UCD}}/{S_{N,GC}} is 1.00 +- 0.44 for the four environments Fornax, Hydra,
Centaurus, and Local Group, which have S_{N,GC} values. This good match also
holds for individual giant galaxies in Fornax and in the Fornax
intracluster-space. The error ranges of the derived UCD specific frequencies in
the various environments then imply that not more than 50% of UCDs were formed
from dwarf galaxies. We show that such a scenario would require >90% of
primordial dwarfs in galaxy cluster centers (<100 kpc) to have been stripped of
their stars. We conclude that the number counts of UCDs are fully consistent
with them being the bright tail of the GC population. From a statistical point
of view there is no need to invoke an additional formation channel. | Observations of environmental quenching in groups in the 11 Gyr since
z=2.5: different quenching for central and satellite galaxies: We present direct observational evidence for star formation quenching in
galaxy groups in the redshift range 0<z<2.5. We utilize a large sample of
nearly 6000 groups, selected by fixed cumulative number density from three
photometric catalogs, to follow the evolving quiescent fractions of central and
satellite galaxies over roughly 11 Gyr. At z~0, central galaxies in our sample
range in stellar mass from Milky Way/M31 analogs (M=6.5x10^10 M\solar) to
nearby massive ellipticals (M=1.5x10^11 M\solar). Satellite galaxies in the
same groups reach masses as low as twice that of the Large Magellanic Cloud
(M=6.5x10^9 M\solar). Using statistical background subtraction, we measure the
average rest-frame colors of galaxies in our groups and calculate the evolving
quiescent fractions of centrals and satellites over seven redshift bins. Our
analysis shows clear evidence for star formation quenching in group halos, with
a different quenching onset for centrals and their satellite galaxies. Using
halo mass estimates for our central galaxies, we find that star formation shuts
off in centrals when typical halo masses reach between 10^12 and 10^13 M\solar,
consistent with predictions from the halo quenching model. In contrast,
satellite galaxies in the same groups most likely undergo quenching by
environmental processes, whose onset is delayed with respect to their central
galaxy. Although star formation is suppressed in all galaxies over time, the
processes that govern quenching are different for centrals and satellites.
While mass plays an important role in determining the star formation activity
of central galaxies, quenching in satellite galaxies is dominated by the
environment in which they reside. |
An independent search for annual modulation and its significance in
ANAIS-112 data: We perform an independent search for sinusoidal-based modulation in the
recently released ANAIS-112 data, which could be induced by dark matter
scatterings. We then evaluate this hypothesis against the null hypothesis that
the data contains only background, using four different model comparison
techniques. These include frequentist, Bayesian, and two information
theory-based criteria (AIC and BIC). This analysis was done on both the
residual data (by subtracting the exponential fit obtained from the ANAIS-112
Collaboration) as well as the total (non-background subtracted) data. We find
that according to the Bayesian model comparison test, the null hypothesis of no
modulation is decisively favored over a cosine-based annual modulation for the
non-background subtracted dataset in 2-6 keV energy range. None of the other
model comparison tests decisively favor any one hypothesis over another. This
is the first application of Bayesian and information theory techniques to test
the annual modulation hypothesis in ANAIS-112 data, extending our previous work
on the DAMA/LIBRA and COSINE-100 data. Our analysis codes have also been made
publicly available. | On the exclusion of intra-cluster plasma from AGN-blown bubbles: Simple arguments suggest that magnetic fields should be aligned tangentially
to the surface of an AGN-blown bubble. If this is the case, charged particles
from the fully ionised intra-cluster medium (ICM) will be prevented,
ordinarily, from crossing the boundary by the Lorentz force. However, recent
observations indicate that thermal material may occupy up to 50% of the volume
of some bubbles. Given the effect of the Lorentz force, the thermal content
must then be attributed to one, or a combination, of the following processes:
i) the entrainment of thermal gas into the AGN outflow that inflated the
bubble; ii) rapid diffusion across the magnetic field lines at the ICM/bubble
interface; iii) magnetic reconnection events which transfer thermal material
across the ICM/bubble boundary. Unless the AGN outflow behaves as a magnetic
tower jet, entrainment may be significant and could explain the observed
thermal content of bubbles. Alternatively, the cross-field diffusion
coefficient required for the ICM to fill a typical bubble is roughly 10^16 cm^2
s^-1, which is anomalously high compared to predictions from turbulent
diffusion models. Finally, the mass transfer rate due to magnetic reconnection
is uncertain, but significant for plausible reconnection rates. We conclude
that entrainment into the outflow and mass transfer due to magnetic
reconnection events are probably the most significant sources of thermal
content in AGN-blown bubbles. |
Detectability of Cosmic Dark Flow in the Type Ia Supernova
Redshift-Distance Relation: We re-analyze the detectability of large scale dark flow (or local bulk flow)
with respect to the CMB background based upon the redshift-distance relation
for Type Ia supernovae (SN Ia). We made two independent analyses: one based
upon identifying the three Cartesian velocity components; and the other based
upon the cosine dependence of the deviation from Hubble flow on the sky. We
apply these analyses to the Union2.1 SN Ia data and to the SDSS-II supernova
survey. For both methods, results for low redshift, $z < 0.05$, are consistent
with previous searches. We find a local bulk flow of $v_{\rm bf} \sim 300$ km
s$^{-1}$ in the direction of $(l,b) \sim (270, 35)^{\circ}$. However, the
search for a dark flow at $z>0.05$ is inconclusive. Based upon simulated data
sets, we deduce that the difficulty in detecting a dark flow at high redshifts
arises mostly from the observational error in the distance modulus. Thus, even
if it exists, a dark flow is not detectable at large redshift with current SN
Ia data sets. We estimate that a detection would require both significant sky
coverage of SN Ia out to $z = 0.3$ and a reduction in the effective distance
modulus error from 0.2 mag to $\lesssim 0.02$ mag. We estimate that a greatly
expanded data sample of $\sim 10^4$ SN Ia might detect a dark flow as small as
300 km s$^{-1}$ out to $z = 0.3$ even with a distance modulus error of $0.2$
mag. This may be achievable in a next generation large survey like LSST. | Carnegie Supernova Project: Observations of Type IIn supernovae: The observational diversity displayed by various Type IIn supernovae (SNe
IIn) is explored and quantified. In doing so, a more coherent picture ascribing
the variety of observed SNe IIn types to particular progenitor scenarios is
sought. Carnegie Supernova Project (CSP) optical and near-infrared light curves
and visual-wavelength spectroscopy of the Type IIn SNe 2005kj, 2006aa, 2006bo,
2006qq, and 2008fq are presented. Combined with previously published
observations of the Type IIn SNe 2005ip and 2006jd, the full CSP sample is used
to derive physical parameters that describe the nature of the interaction
between the expanding SN ejecta and the circumstellar material (CSM). For each
SN of our sample, we find counterparts, identifying objects similar to SNe
1994W (SN 2006bo), 1998S (SN 2008fq), and 1988Z (SN 2006qq). We present the
unprecedented initial $u$-band plateau of SN 2006aa, and its peculiar late-time
luminosity and temperature evolution. For each SN, mass-loss rates of
10$^{-4}-10^{-2}$ $M_{\odot}$ yr$^{-1}$ are derived, assuming the CSM was
formed by steady winds. Typically wind velocities of a few hundred km s$^{-1}$
are also computed. The CSP SN IIn sample seems to be divided into subcategories
rather than to have exhibited a continuum of observational properties. The wind
and mass-loss parameters would favor a luminous blue variable progenitor
scenario. However the assumptions made to derive those parameters strongly
influence the results, and therefore, other progenitor channels behind SNe IIn
cannot be excluded at this time. |
Gravitational Waves from Binary Mergers of Sub-solar Mass Dark Black
Holes: We explore the possible spectrum of binary mergers of sub-solar mass black
holes formed out of dark matter particles interacting via a dark
electromagnetism. We estimate the properties of these dark black holes by
assuming that their formation process is parallel to Population-III star
formation; except that dark molecular cooling can yield smaller opacity limit.
We estimate the binary coalescence rates for the Advanced LIGO and Einstein
telescope, and find that scenarios compatible with all current constraints
could produce dark black holes at rates high enough for detection by Advanced
LIGO. | A short mean free path at $z=6$ favors late and rapid reionization by
faint galaxies: Recent measurements of the ionizing photon mean free path
($\lambda_{912}^{\rm mfp}$) at $5 < z < 6$ suggest that the IGM was rapidly
evolving at those times. We use radiative transfer simulations to explore the
implications for reionization, with a focus on the short value of
$\lambda_{912}^{\rm mfp} = 3.57^{+3.09}_{-2.14}$ cMpc/$h$ at $z=6$. We
introduce a model for sub-resolution ionizing photon sinks based on radiative
hydrodynamics simulations of small-scale IGM clumping. We argue that the rapid
evolution in $\lambda_{912}^{\rm mfp}$ at $z=5-6$, together with constraints on
the metagalactic ionizing background, favors a late reionization process in
which the neutral fraction evolved rapidly in the latter half. We also argue
that the short $\lambda_{912}^{\rm mfp}(z=6)$ points to faint galaxies as the
primary drivers of reionizaton. Our preferred model, with $\lambda_{912}^{\rm
mfp}(z=6) = 6.5$ Mpc/$h$, has a midpoint of $z= 7.1$ and ends at $z= 5.1$. It
requires 3 ionizing photons per H atom to complete reionization and a LyC
photon production efficiency of $\log(f^{\rm eff}_{\rm esc} \xi_{\rm
ion}/[\mathrm{erg}^{-1} \mathrm{Hz}]) = 24.8$ at $z>6$. Recovering
$\lambda_{912}^{\rm mfp}(z=6)$ as low as the measured central value may require
an increase in IGM clumpiness beyond predictions from simulations, with a
commensurate increase in the photon budget. |
Simulations of MHD Instabilities in Intracluster Medium Including
Anisotropic Thermal Conduction: We perform a suite of simulations of cooling cores in clusters of galaxies in
order to investigate the effect of the recently discovered heat flux buoyancy
instability (HBI) on the evolution of cores. Our models follow the
3-dimensional magnetohydrodynamics (MHD) of cooling cluster cores and capture
the effects of anisotropic heat conduction along the lines of magnetic field,
but do not account for the cosmological setting of clusters or the presence of
AGN. Our model clusters can be divided into three groups according to their
final thermodynamical state: catastrophically collapsing cores, isothermal
cores, and an intermediate group whose final state is determined by the initial
configuration of magnetic field. Modeled cores that are reminiscent of real
cluster cores show evolution towards thermal collapse on a time scale which is
prolonged by a factor of ~2-10 compared with the zero-conduction cases. The
principal effect of the HBI is to re-orient field lines to be perpendicular to
the temperature gradient. Once the field has been wrapped up onto spherical
surfaces surrounding the core, the core is insulated from further conductive
heating (with the effective thermal conduction suppressed to less than 1/100th
of the Spitzer value) and proceeds to collapse. We speculate that, in real
clusters, the central AGN and possibly mergers play the role of "stirrers,"
periodically disrupting the azimuthal field structure and allowing thermal
conduction to sporadically heat the core. | Revisiting Cardassian Model and Cosmic Constraint: In this paper, we revisit the Cardassian model in which the radiation energy
component is included. It is important for early epoch when the radiation
cannot be neglected because the equation of state (EoS) of the effective dark
energy becomes time variable. Therefore, it is not equivalent to the
quintessence model with a constant EoS anymore. This situation was almost
overlooked in the literature. By using the recent released Union2 557 of type
Ia supernovae (SN Ia), the baryon acoustic oscillation (BAO) from Sloan Digital
Sky Survey and the WiggleZ data points, the full information of cosmic
microwave background (CMB) measurement given by the seven-year Wilkinson
Microwave Anisotropy Probe observation, we constrain the Cardassian model via
the Markov Chain Monte Carlo (MCMC) method. A tight constraint is obtained: $n=
-0.0479_{- 0.0732- 0.148}^{+ 0.0730+ 0.142}$ in $1,2\sigma$ regions. The
deviation of Cardassian model from quintessence model is shown in CMB
anisotropic power spectra at high l's parts due to the evolution of EoS. But it
is about the order of 0.1% which cannot be discriminated by current data sets.
The Cardassian model is consistent with current cosmic observational data sets. |
Transient dark energy, cosmological constant boundary crossing and dark
energy $w(z)$ data fits: The formalism of dark energy based on modeling speed of sound as a function
of equation of state parameter is elaborated. A specific model which allows
detailed study of cosmological constant boundary crossing is introduced and
analytical solutions for the model dynamics are obtained. It is shown how in
specific parameter regimes dark energy can be a transient phenomenon. It is
further demonstrated how the model reproduces specific features of recent fits
of dark energy $w(z)$ to observational data. | Phase Transition Generated Cosmological Magnetic Field at Large Scales: We constrain a primordial magnetic field (PMF) generated during a phase
transition (PT) using the big bang nucleosynthesis bound on the relativistic
energy density. The amplitude of the PMF at large scales is determined by the
shape of the PMF spectrum outside its maximal correlation length scale. Even if
the amplitude of the PMF at 1 Mpc is small, PT-generated PMFs can leave
observable signatures in the potentially detectable relic gravitational wave
background if a large enough fraction ($1-10%$) of the thermal energy is
converted into the PMF. |
The Effects of an AGN on Host Galaxy Colour and Morphology Measurements: We assess the effects of simulated active galactic nuclei (AGNs) on the
colour and morphology measurements of their host galaxies. To test the
morphology measurements, we select a sample of galaxies not known to host AGNs
and add a series of point sources scaled to represent specified fractions of
the observed V band light detected from the resulting systems; we then compare
morphology measurements of the simulated systems to measurements of the
original galaxies. AGN contributions >20 per cent bias most of the morphology
measurements tested, though the extent of the apparent bias depends on the
morphological characteristics of the original galaxies. We test colour
measurements by adding to non-AGN galaxy spectra a quasar spectrum scaled to
contribute specified fractions of the rest-frame B band light detected from the
resulting systems. A quasar fraction of 5 per cent can move the NUV-r colour of
an elliptical galaxy from the UV-optical red sequence to the green valley, and
20 per cent can move it into the blue cloud. Combining the colour and
morphology results, we find that a galaxy/AGN system with an AGN contribution
>20 per cent may appear bluer and more bulge-dominated than the underlying
galaxy. We conclude that (1) bulge-dominated, E/S0/Sa, and early-type
morphology classifications are accurate for red AGN host galaxies and may be
accurate for blue host galaxies, unless the AGN manifests itself as a
well-defined point source; and (2) although highly unobscured AGNs, such as the
quasar used for our experiments, can significantly bias the measured colours of
AGN host galaxies, it is possible to identify such systems by examining optical
images of the hosts for the presence of a point source and/or measuring the
level of nuclear obscuration. | Non-linear Fields in Generalized Cosmologies: The perturbative approach to structure formation has recently received a lot
of attention in the literature. In such setups the final predictions for
observables like the power spectrum is often derived under additional
approximations such as a simplified time dependence. Here we provide all-order
perturbative integral solutions for density and velocity fields in generalized
cosmologies, with a direct application to clustering quintessence. We go beyond
the standard results based on extending the EdS-like approximations. As an
illustrative example, we apply our findings to the calculation of the one-loop
power spectrum of density and momentum fields. We find corrections close to
$1\%$ in the mildly non-linear regime of $\Lambda$CDM cosmologies for the
density power spectrum, while in the case of the density-momentum power
spectrum effects can reach up to $1.5\%$ for $k\sim 0.2h/$Mpc. |
Cosmic opacity: cosmological-model-independent tests from gravitational
waves and Type Ia Supernova: In this paper, we present a scheme to investigate the opacity of the Universe
in a cosmological-model-independent way, with the combination of current and
future available data in gravitational wave (GW) and electromagnetic (EM)
domain. In the FLRW metric, GWs propagate freely through a perfect fluid
without any absorption and dissipation, which provides a distance measurement
unaffected by the cosmic opacity. Focusing on the simulated data of
gravitational waves from the third-generation gravitational wave detector (the
Einstein Telescope, ET), as well as the newly-compiled SNe Ia data (JLA and
Pantheon sample), we find an almost transparent universe is strongly favored at
much higher redshifts ($z\sim 2.26$). Our results suggest that, although the
tests of cosmic opacity are not significantly sensitive to its parametrization,
a strong degeneracy between the cosmic opacity parameter and the absolute
\textit{B}-band magnitude of SNe Ia is revealed in this analysis. More
importantly, we obtain that future measurements of the luminosity distances of
gravitational waves sources will be much more competitive than the current
analyses, which makes it expectable more vigorous and convincing constraints on
the cosmic opacity (and consequently on background physical mechanisms) and a
deeper understanding of the intrinsic properties of type Ia supernovae in a
cosmological-model-independent way. | The Role of Groups in Galaxy Evolution: compelling evidence of
pre-processing out to the turnaround radius of clusters: We present clear and direct evidence of the pre-processing effect of group
galaxies falling into clusters in the local Universe ($z \lesssim 0.1$). We
start with a sample of 238 clusters, from which we select 153 with N$_{200}
\ge$ 20. We considered 1641 groups within the turnaround radius ($\sim$
5$\times$R$_{200}$) of these 153 clusters. There are 6654 {\it individual
cluster galaxies} and 4133 {\it group galaxies} within this radius. We
considered two control samples of galaxies, in isolated groups and in the
field. The first comprises 2601 galaxies within 1606 {\it isolated groups}, and
the latter has 4273 field objects. The fraction of star forming galaxies in
infalling groups has a distinct clustercentric behavior in comparison to the
remaining cluster galaxies. Even at $5 \times $R$_{200}$ the {\it group
galaxies} already show a reduced fraction of star forming objects. At this
radius, the results for the {\it individual cluster galaxies} is actually
compatible to the field. That is strong evidence that the group environment is
effective to quench the star formation prior to the cluster arrival. The group
star forming fraction remains roughly constant inwards, decreasing
significantly only within the cluster R$_{200}$ radius. We have also found that
the pre-processing effect depends on the group mass (indicated by the number of
members). The effect is larger for more massive groups. However, it is
significant even for pairs an triplets. Finally, we find evidence that the time
scale required for morphological transformation is larger than the one for
quenching. |
NGC 6340: an old S0 galaxy with a young polar disc. Clues from
morphology, internal kinematics and stellar populations: Lenticular galaxies are believed to form by a combination of environmental
effects and secular evolution. We study the nearby disc-dominated S0 galaxy NGC
6340 photometrically and spectroscopically to understand the mechanisms of S0
formation and evolution in groups. We use SDSS images to build colour maps and
light profile of NGC 6340 which we decompose using a three-component model
including Sersic and two exponential profiles. We also use Spitzer images to
study the morphology of regions containing warm ISM and dust. Then, we
re-process and re-analyse deep long-slit spectroscopic data for NGC 6340 and
recover its stellar and gas kinematics, distribution of age and metallicity
with the NBursts full spectral fitting. We obtain the profiles of internal
kinematics, age, and metallicity out to >2 half-light radii. The three
structural components of NGC 6340 are found to have distinct kinematical and
stellar population properties. We see a kinematical misalignment between inner
and outer regions of the galaxy. We confirm the old metal-rich centre and a
wrapped inner gaseous polar disc (r~1 kpc) having weak ongoing star formation,
counter-rotating in projection with respect to the stars. The central compact
pseudo-bulge of NGC 6340 looks very similar to compact elliptical galaxies. In
accordance with the results of numerical simulations, we conclude that
properties of NGC 6340 can be explained as the result of a major merger of
early-type and spiral galaxies which occurred about 12 Gyr ago. The
intermediate exponential structure might be a triaxial pseudo-bulge formed by a
past bar structure. The inner compact bulge could be the result of a nuclear
starburst triggered by the merger. The inner polar disc appeared recently,
1/3-1/2 Gyr ago as a result of another minor merger or cold gas accretion. | Deep 1.1 mm-wavelength imaging of the GOODS-South field by AzTEC/ASTE --
II. Redshift distribution and nature of the submillimetre galaxy population: We report the results of the counterpart identification and a detailed
analysis of the physical properties of the 48 sources discovered in our deep
1.1mm wavelength imaging survey of the GOODS-South field using the AzTEC
instrument on the Atacama Submillimeter Telescope Experiment (ASTE). One or
more robust or tentative counterpart candidate is found for 27 and 14 AzTEC
sources, respectively, by employing deep radio continuum, Spitzer MIPS & IRAC,
and LABOCA 870 micron data. Five of the sources (10%) have two robust
counterparts each, supporting the idea that these galaxies are strongly
clustered and/or heavily confused. Photometric redshifts and star formation
rates (SFRs) are derived by analyzing UV-to-optical and IR-to-radio SEDs. The
median redshift of z~2.6 is similar to other earlier estimates, but we show
that 80% of the AzTEC-GOODS sources are at z>2, with a significant high
redshift tail (20% at z>3.3). Rest-frame UV and optical properties of AzTEC
sources are extremely diverse, spanning 10 magnitude in the i- and K-band
photometry with median values of i=25.3 and K=22.6 and a broad range of red
colour (i-K=0-6). These AzTEC sources are some of the most luminous galaxies in
the rest-frame optical bands at z>2, with inferred stellar masses of (1-30) x
10^{10} solar masses and UV-derived star formation rates of SFR(UV) > 10-1000
solar masses per year. The IR-derived SFR, 200-2000 solar masses per year, is
independent of redshift or stellar mass. The resulting specific star formation
rates, SSFR = 1-100 per Gyr, are 10-100 times higher than similar mass galaxies
at z=0, and they extend the previously observed rapid rise in the SSFR with
redshift to z=2-5. These galaxies have a SFR high enough to have built up their
entire stellar mass within their Hubble time. We find only marginal evidence
for an AGN contribution to the near-IR and mid-IR SEDs. (abridged) |
Lyth bound revisited: Imposing that the excursion distance of inflaton in field space during
inflation be less than the Planck scale, we derive an upper bound on the
tensor-to-scalar ratio at the CMB scales, i.e. $r_{*,max}$, in the general
canonical single-field slow-roll inflation model, in particular the model with
non-negligible running of the spectral index $\alpha_s$ and/or the running of
running $\beta_s$. We find that $r_{*,max}\simeq 7\times 10^{-4}$ for
$n_s=0.9645$ without running and running of running, and $r_{*,max}$ is
significantly relaxed to the order of ${\cal O}(10^{-2}\sim 10^{-1})$ in the
inflation model with $\alpha_s$ and/or $\beta_s\sim +{\cal O}(10^{-2})$ which
are marginally preferred by the Planck 2015 data. | The Galaxy Cluster Concentration-Mass Scaling Relation: Scaling relations of clusters have made them particularly important
cosmological probes of structure formation. In this work, we present a
comprehensive study of the relation between two profile observables,
concentration ($\mathrm{c_{vir}}$) and mass ($\mathrm{M_{vir}}$). We have
collected the largest known sample of measurements from the literature which
make use of one or more of the following reconstruction techniques: Weak
gravitational lensing (WL), strong gravitational lensing (SL), Weak+Strong
Lensing (WL+SL), the Caustic Method (CM), Line-of-sight Velocity Dispersion
(LOSVD), and X-ray. We find that the concentration-mass (c-M) relation is
highly variable depending upon the reconstruction technique used. We also find
concentrations derived from dark matter only simulations (at approximately
$\mathrm{M_{vir} \sim 10^{14} M_{\odot}}$) to be inconsistent with the WL and
WL+SL relations at the $\mathrm{1\sigma}$ level, even after the projection of
triaxial halos is taken into account. However, to fully determine consistency
between simulations and observations, a volume-limited sample of clusters is
required, as selection effects become increasingly more important in answering
this. Interestingly, we also find evidence for a steeper WL+SL relation as
compared to WL alone, a result which could perhaps be caused by the varying
shape of cluster isodensities, though most likely reflects differences in
selection effects caused by these two techniques. Lastly, we compare
concentration and mass measurements of individual clusters made using more than
one technique, highlighting the magnitude of the potential bias which could
exist in such observational samples. |
Tachyon stars: We consider a self-gravitating body composed of ideal Fermi gas of tachyons
at zero temperature. The Oppenheimer-Volkoff equation is solved for various
central densities and various tachyon mass parameter $m$. Although a pure
tachyon star has finite mass, it cannot occur in nature because the equilibrium
condition P=0 and the causality condition cannot be satisfied simultaneously. A
stable configuration with tachyon content must be covered with a non-tachyon
envelope. The boundary between the tachyon core and the envelope is determined
by the critical pressure $P_T$, which depends on the tachyon mass $m$. The
tachyon core is dominant and its mass can exceed many times the solar mass
$M_{\odot}$ when $m$ is much smaller than the nucleon mass $m_p$, while at
large $m$ compared with $m_p$, the main contribution to the total stellar mass
is due to the envelope whose material determines the parameters of the whole
star. However, the parameters of the tachyon core do not depend on the envelope
material. When the tachyon core appears, its mass $M_T$ and radius $r_T$ grow
up with increasing central density until maximum values are reached, after
which the mass and radius slowly decrease. The redshift at the surface of the
tachyon core does not depend on $m$ and never exceeds $z_{\max}\simeq 0.3$. The
maximum mass of tachyon core and its maximum radius are achieved at certain
central density and obey universal formulas $M_{T\max}/M_{\odot}=0.52m_p^2/m^2$
and $r_{T\max}=4.07m_p^2/m^2$ [km] that allow to estimate arbitrary
supermassive tachyonic bodies at the cosmological scale. | Probing reionization using quasar near-zones at redshift z ~ 6: Using hydrodynamical simulations coupled to a radiative transfer code, we
study the additional heating effects in the intergalactic medium (IGM) produced
by $z\sim 6$ quasars in their near-zones. If helium is predominantly in HeII to
begin with, both normalization ($T_0$) and slope ($\gamma$) of the IGM
effective equation-of-state get modified by the excess ionization from the
quasars. Using the available constraints on $T_0$ at $z\sim6$, we discuss
implications for the nature and epoch of HI and HeII reionization. We study the
extent of the HeIII region as a function of quasar age and show, for a typical
inferred age of $z \sim 6$ quasars (i.e. $\sim 10^8$ yrs), it extends up to 80%
of the HI proximity region. For these long lifetimes, the heating effects can
be detected even when all the HI lines from the proximity region are used.
Using the flux and curvature probability distribution functions (PDFs), we
study the statistical detectability of heating effects as a function of initial
physical conditions in the IGM. For the present sample size, cosmic variance
dominates the flux PDF. The curvature statistics is more suited to capturing
the heating effects beyond the cosmic variance, even if the sample size is half
of what is presently available. |
Inflation models in the light of self-interacting sterile neutrinos: Short baseline neutrino experiments, like LSND and MiniBooNE experiments,
pointed towards the existence of eV mass scale sterile neutrinos. To reconcile
sterile neutrinos with cosmology self interaction between sterile neutrinos has
been studied. We analysed Planck cosmic microwave background (CMB) data with
self-interacting sterile neutrino (SI$\nu$) and study their impact on inflation
models. The fit to the CMB data in SI$\nu$ model is as good as the fit to
$\Lambda$CDM model. We find that the spectral index ($n_s$) values shift to
$0.9361\pm 0.0055$ in SI$\nu$ model. This has significant impact on the
validity of different inflation models. For example the Starobinsky and quartic
hilltop model, which were allowed within $\Lambda$CDM cosmology, are ruled out.
On the other hand some models like natural and Coleman-Weinberg inflation are
now favoured. Therefore, the existence of self interacting sterile neutrinos
with eV order of mass will play an important role in the selection of correct
inflation model. | Large-Scale Structure in Brane-Induced Gravity I. Perturbation Theory: We study the growth of subhorizon perturbations in brane-induced gravity
using perturbation theory. We solve for the linear evolution of perturbations
taking advantage of the symmetry under gauge transformations along the
extra-dimension to decouple the bulk equations in the quasistatic
approximation, which we argue may be a better approximation at large scales
than thought before. We then study the nonlinearities in the bulk and brane
equations, concentrating on the workings of the Vainshtein mechanism by which
the theory becomes general relativity (GR) at small scales. We show that at the
level of the power spectrum, to a good approximation, the effect of
nonlinearities in the modified gravity sector may be absorbed into a
renormalization of the gravitational constant. Since the relation between the
lensing potential and density perturbations is entirely unaffected by the extra
physics in these theories, the modified gravity can be described in this
approximation by a single function, an effective gravitational constant for
nonrelativistic motion that depends on space and time. We develop a resummation
scheme to calculate it, and provide predictions for the nonlinear power
spectrum. At the level of the large-scale bispectrum, the leading order
corrections are obtained by standard perturbation theory techniques, and show
that the suppression of the brane-bending mode leads to characteristic
signatures in the non-Gaussianity generated by gravity, generic to models that
become GR at small scales through second-derivative interactions. We compare
the predictions in this work to numerical simulations in a companion paper. |
KiDS-1000 Cosmology: constraints beyond flat $Λ$CDM: We present constraints on extensions to the flat $\Lambda$CDM cosmological
model by varying the spatial curvature $\Omega_K$, the sum of the neutrino
masses $\sum m_\nu$, the dark energy equation of state parameter $w$, and the
Hu-Sawicki $f(R)$ gravity $f_{R0}$ parameter. With the combined $3\times2$pt
measurements of cosmic shear from the Kilo-Degree Survey (KiDS-1000), galaxy
clustering from the Baryon Oscillation Spectroscopic Survey (BOSS), and
galaxy-galaxy lensing from the overlap between KiDS-1000, BOSS, and the
spectroscopic 2-degree Field Lensing Survey (2dFLenS), we find results that are
fully consistent with a flat $\Lambda$CDM model with
$\Omega_K=0.011^{+0.054}_{-0.057}$, $\sum m_\nu<1.76$ eV (95% CL), and
$w=-0.99^{+0.11}_{-0.13}$. The $f_{R0}$ parameter is unconstrained in our fully
non-linear $f(R)$ cosmic shear analysis. Considering three different model
selection criteria, we find no clear preference for either the fiducial flat
$\Lambda$CDM model or any of the considered extensions. Besides extensions to
the flat $\Lambda$CDM parameter space, we also explore restrictions to common
subsets of the flat $\Lambda$CDM parameter space by fixing the amplitude of the
primordial power spectrum to the Planck best-fit value, as well as adding
external data from supernovae and lensing of the CMB. Neither the
beyond-$\Lambda$CDM models nor the imposed restrictions explored in this
analysis are able to resolve the $\sim 3\sigma$ tension in $S_8$ between the
$3\times2$pt constraints and Planck, with the exception of $w$CDM, where the
$S_8$ tension is resolved. The tension in the $w$CDM case persists, however,
when considering the joint $S_8$-$w$ parameter space. The joint flat
$\Lambda$CDM CMB lensing and $3\times2$pt analysis is found to yield tight
constraints on $\Omega_{\rm m}=0.307^{+0.008}_{-0.013}$,
$\sigma_8=0.769^{+0.022}_{-0.010}$, and $S_8=0.779^{+0.013}_{-0.013}$. | TDCOSMO X. Automated Modeling of 9 Strongly Lensed Quasars and
Comparison Between Lens Modeling Software: To use strong gravitational lenses as an astrophysical or cosmological probe,
models of their mass distributions are often needed. We present a new,
time-efficient automation code for uniform modeling of strongly lensed quasars
with GLEE, a lens modeling software, for high-resolution multi-band data. By
using the observed positions of the lensed quasars and the spatially extended
surface brightness distribution of the lensed quasar host galaxy, we obtain a
model of the mass distribution of the lens galaxy. We apply this uniform
modeling pipeline to a sample of nine strongly lensed quasars with HST WFC 3
images. The models show in most cases well reconstructed light components and a
good alignment between mass and light centroids. We find that the automated
modeling code significantly reduces the user input time during the modeling
process. The preparation time of required input files is reduced significantly.
This automated modeling pipeline can efficiently produce uniform models of
extensive lens system samples which can be used for further cosmological
analysis. A blind test through a comparison with the results of an independent
automated modeling pipeline based on the modeling software Lenstronomy reveals
important lessons. Quantities such as Einstein radius, astrometry, mass
flattening and position angle are generally robustly determined. Other
quantities depend crucially on the quality of the data and the accuracy of the
PSF reconstruction. Better data and/or more detailed analysis will be necessary
to elevate our automated models to cosmography grade. Nevertheless, our
pipeline enables the quick selection of lenses for follow-up monitoring and
further modeling, significantly speeding up the construction of
cosmography-grade models. This is an important step forward to take advantage
of the orders of magnitude increase in the number of lenses expected in the
coming decade. |
Emission line - radio correlation for Low Luminosity Compact sources.
Evolution schemes: We present radio and optical analysis of a sample of Low Luminosity Compact
(LLC) objects, selected from FIRST survey and observed with MERLIN at L-band
and C-band. The main criterion used for selection was luminosity of the objects
and approximately one third of the CSS sources from the new sample have a value
of radio luminosity comparable to FR\,Is.The analysis of a radio properties of
LLC sources show they occupy the space in radio power versus linear size
diagram below the main evolutionary path of radio objects. We suggest that many
of them might be short-lived objects, and their radio emission may be disrupted
several times before becoming FR\,IIs. The optical analysis of the LLC sources
were made based on the available SDSS images and spectra. We have classified
the sources as high and low excitation galaxies (HEG and LEG, respectively).
The optical and radio properties of the LLC sample are in general consistent
with brighter CSSs and large-scale radio sources. However, when LLC are added
to the other samples, HEG and LEG seem to follow independent, parallel
evolutionary tracks. LLC and luminous CSS behave like FR\,II sources, while
FR\,I seem to belong to a different group of objects, concerning ionization
mechanisms. Based on our results, we propose the independent, parallel
evolutionary tracks for HEG and LEG sources, evolving from GPS - CSS - FR. | Early structure formation from cosmic string loops: We examine the effects of cosmic strings on structure formation and on the
ionization history of the universe. While Gaussian perturbations from inflation
are known to provide the dominant contribution to the large scale structure of
the universe, density perturbations due to strings are highly non-Gaussian and
can produce nonlinear structures at very early times. This could lead to early
star formation and reionization of the universe. We improve on earlier studies
of these effects by accounting for high loop velocities and for the filamentary
shape of the resulting halos. We find that for string energy scales G\mu >
10^{-7} the effect of strings on the CMB temperature and polarization power
spectra can be significant and is likely to be detectable by the Planck
satellite. We mention shortcomings of the standard cosmological model of galaxy
formation which may be remedied with the addition of cosmic strings, and
comment on other possible observational implications of early structure
formation by strings. |
Finding Rare AGN: XMM-Newton and Chandra Observations of SDSS Stripe 82: We have analyzed the {\it XMM-Newton} and {\it Chandra} data overlapping
$\sim$16.5 deg$^2$ of Sloan Digital Sky Survey Stripe 82, including $\sim$4.6
deg$^2$ of proprietary {\it XMM-Newton} data that we present here. In total,
3362 unique X-ray sources are detected at high significance. We derive the {\it
XMM-Newton} number counts and compare them with our previously reported {\it
Chandra} Log$N$-Log$S$ relations and other X-ray surveys. The Stripe 82 X-ray
source lists have been matched to multi-wavelength catalogs using a maximum
likelihood estimator algorithm. We discovered the highest redshift ($z=5.86$)
quasar yet identified in an X-ray survey. We find 2.5 times more high
luminosity (L$_x \geq 10^{45}$ erg s$^{-1}$) AGN than the smaller area {\it
Chandra} and {\it XMM-Newton} survey of COSMOS and 1.3 times as many identified
by XBo\"otes. Comparing the high luminosity AGN we have identified with those
predicted by population synthesis models, our results suggest that this AGN
population is a more important component of cosmic black hole growth than
previously appreciated. Approximately a third of the X-ray sources not detected
in the optical are identified in the infrared, making them candidates for the
elusive population of obscured high luminosity AGN in the early universe. | Toward the low-scatter selection of X-ray clusters: Galaxy cluster
detection with eROSITA through cluster outskirts: One key ingredient in using galaxy clusters (GCs) as a precision cosmological
probe in large X-ray surveys is to understand selection effects. The dependence
of the X-ray emission on the square of the gas density leads to a predominant
role of cool cores in the detection of GCs. The contribution of cool cores to
the X-ray luminosity does not scale with GC mass and cosmology and therefore
affects the use of X-ray GCs in producing cosmological constraints. One of the
main science goals of the eROSITA mission is to constrain cosmology with a wide
X-ray survey. We propose an eROSITA GC detection scheme that avoids the use of
X-ray GC centers in detection. We calculate theoretical expectations and
characterize the performance of this scheme by simulations. Performing
realistic simulations of point sources (PSs) in survey mode we search for
spatial scales where the extended signal is uncontaminated by the PS flux. We
derive a combination of scales and thresholds, which result in a clean extended
source catalog. We design the output of the GC detection which enables
calibrating the core-excised luminosity using external mass measurements. We
provide a way to incorporate the results of this calibration in the production
of final core-excised luminosity. Similarly to other GC detection pipelines, we
sample the flux - core radius detection space of our method and find many
similarities with the pipeline used in the 400d survey. Both detection methods
require large statistics on compact GCs, in order to reduce the contamination
from PSs. The benefit of our pipeline consists in the sensitivity to the outer
GC shapes, which are characterized by large core sizes with little GC to GC
variation at a fixed total mass. GC detection through cluster outskirts
improves the GC characterization using eROSITA survey data and is expected to
yield well characterized GC catalogs having simple selection functions. |
High resolution spectroscopy of the three dimensional cosmic web with
close QSO groups: We study the three-dimensional distribution of matter at z~2 using high
resolution spectra of QSO pairs and simulated spectra drawn from cosmological
hydro-dynamical simulations. We present a sample of 15 QSOs, corresponding to
21 baselines of angular separations evenly distributed between ~1 and 14
arcmin, observed with the Ultraviolet and Visual Echelle Spectrograph (UVES) at
the European Southern Observatory-Very Large Telescope (ESO-VLT). The observed
correlation functions of the transmitted flux in the HI Lya forest transverse
to and along the line of sight are in agreement, implying that the distortions
in redshift space due to peculiar velocities are relatively small and - within
the relatively large error bars - not significant. The clustering signal is
significant up to velocity separations of ~300 km/s, corresponding to about 5
h^{-1} comoving Mpc. Compatibility at the 2 sigma level has been found both for
the Auto- and Cross-correlation functions and for the set of the Cross
correlation coefficients. The analysis focuses in particular on two QSO groups
of the sample. Searching for alignments in the redshift space between Lya
absorption lines belonging to different lines of sight, it has been possible to
discover the presence of a wide HI structures extending over about ten Mpc in
comoving space, and give constraints on the sizes of two cosmic under-dense
regions in the intergalactic medium. | A SAURON study of dwarf elliptical galaxies in the Virgo Cluster: Dwarf elliptical galaxies are the most common galaxy type in nearby galaxy
clusters, yet they remain relatively poorly studied objects and many of their
basic properties have yet to be quantified. In this contribution we present the
preliminary results of a study of 4 Virgo and 1 field galaxy obtained with the
SAURON integral field unit on the William Herschel Telescope (La Palma). While
traditional long-slit observations are likely to miss more complicated
kinematic features, with SAURON we are able to study both kinematics and
stellar populations in two dimensions, obtaining a much more detailed view of
the mass distribution and star formation histories. |
Sunyaev-Zel'dovich contribution in CMB analysis: The Sunyaev-Zel'dovich (SZ) effect has long been identified as one of the
most important secondary effects of the Cosmic Microwave Background (CMB). On
the one hand, it is a potentially very powerful cosmological probe providing us
with additional constraints and on the other hand it represents the major
source of secondary fluctuations at small angular scales (l > 1000). We
investigate the effects of the SZ modelling in the determination of the
cosmological parameters. We explore the consequences of the SZ power spectrum
computation by comparing three increasingly complex modelling, from a fixed
template with an amplitude factor to a calculation including the full
cosmological parameter dependency. We also examine the dependency of the
cosmological parameter estimation on the intra-cluster gas description used to
calculate the SZ spectrum. We show that methods assuming an SZ template bias
the cosmological parameters (by up to 2 sigmas on sigma_8) when the cosmology
used in the template deviates from the reference one. A joint CMB-SZ analysis
with a full cosmological dependency of the SZ spectrum does not suffer from
such biases and moreover improves the confidence intervals of sigma_8 and
Omega_{dm}h^2 (2.5 and 2 times respectively) with respect to a pure CMB
analysis. However, the latter method is quite sensitive to the intra-cluster
gas parameters and hence requires extra information on the clusters to
alleviate the induced biases. | Enhanced accretion rates of stars on Super-massive Black Holes by
star-disk interactions in galactic nuclei: We investigate the dynamical interaction of a central star cluster
surrounding a super-massive black hole and a central accretion disk. The
dissipative force acting on stars in the disk leads to an enhanced mass flow
towards the super-massive black hole and to an asymmetry in the phase space
distribution due to the rotating accretion disk. The accretion disk is
considered as a stationary Keplerian rotating disk, which is vertically
extended in order to employ a fully self-consistent treatment of stellar
dynamics including the dissipative force originating from star-gas ram pressure
effects. The stellar system is treated with a direct high-accuracy N-body
integration code. A star-by-star representation, desirable in N-body
simulations, cannot be extended to real particle numbers yet. Hence, we
carefully discuss the scaling behavior of our model with regard to particle
number and tidal accretion radius. The main idea is to find a family of models
for which the ratio of two-body relaxation time and dissipation time (for
kinetic energy of stellar orbits) is constant, which then allows us to
extrapolate our results to real parameters of galactic nuclei. Our model is
derived from basic physical principles and as such it provides insight into the
role of physical processes in galactic nuclei, but it should be regarded as a
first step towards more realistic and more comprehensive simulations.
Nevertheless, the following conclusions appear to be robust: the star accretion
rate onto the accretion disk and subsequently onto the super-massive black hole
is enhanced by a significant factor compared to purely stellar dynamical
systems neglecting the disk. This process leads to enhanced fueling of central
disks in active galactic nuclei and to an enhanced rate of tidal stellar
disruptions. [Abridged] |
The MillenniumTNG Project: The large-scale clustering of galaxies: Modern redshift surveys are tasked with mapping out the galaxy distribution
over enormous distance scales. Existing hydrodynamical simulations, however, do
not reach the volumes needed to match upcoming surveys. We present results for
the clustering of galaxies using a new, large volume hydrodynamical simulation
as part of the MillenniumTNG (MTNG) project. With a computational volume that
is $\approx15$ times larger than the next largest such simulation currently
available, we show that MTNG is able to accurately reproduce the observed
clustering of galaxies as a function of stellar mass. When separated by colour,
there are some discrepancies with respect to the observed population, which can
be attributed to the quenching of satellite galaxies in our model. We combine
MTNG galaxies with those generated using a semi-analytic model to emulate the
sample selection of luminous red galaxies (LRGs) and emission line galaxies
(ELGs), and show that although the bias of these populations is approximately
(but not exactly) constant on scales larger than $\approx10$ Mpc, there is
significant scale-dependent bias on smaller scales. The amplitude of this
effect varies between the two galaxy types, and also between the semi-analytic
model and MTNG. We show that this is related to the distribution of haloes
hosting LRGs and ELGs. Using mock SDSS-like catalogues generated on MTNG
lightcones, we demonstrate the existence of prominent baryonic acoustic
features in the large-scale galaxy clustering. We also demonstrate the presence
of realistic redshift space distortions in our mocks, finding excellent
agreement with the multipoles of the redshift-space clustering measured in SDSS
data. | Velocities hasten to tell us about the Universe: The peculiar velocities of galaxies are driven by gravity, and hence hold the
promise of probing details of how gravity forms structures. In particular it is
possible to constrain cosmological parameters and to test extensions to the
standard model, such as modifications to the theory of gravity or the existence
of primordial density perturbations which are non-Gaussian. This constraining
power has been frustrated by systematic effects, but we appear to be entering
an era when velocity measurements may finally be living up to their promise. |
The Effects of Lyman-Limit Systems on the Evolution and Observability of
the Epoch of Reionization: We present the first large-scale, full radiative transfer simulations of the
reionization of the intergalactic medium in the presence of Lyman-limit systems
(LLSs). To illustrate the impact of LLS opacity, possibly missed by previous
simulations, we add either a uniform or spatially-varying hydrogen bound-free
opacity. This opacity, implemented as the mean free path (mfp) of the ionizing
photons, extrapolates the observed, post-reionization redshift dependence into
the epoch of reionization. In qualitative agreement with previous studies, we
find that at late times the presence of LLSs slows down the ionization fronts,
and alters the size distribution of H II regions. We quantitatively
characterize the size distribution and morphological evolution of H II regions
and examine the effects of the LLSs on the redshifted 21-cm signal from the
patchy reionization. The presence of LLSs extends the ionization history by
$\Delta z \sim 0.8$. The LLS absorbers significantly impede the late-time
growth of the H II regions. The position dependent LLS distribution slows
reionization further and additionally limits the late growth of the ionized
regions. However, there is no "freeze out" of the H II regions and the largest
regions grow to the size of the simulation volume. The 21-cm power spectra show
that at large scales the power drops by a factor of 2 for 50% and 75%
ionization stages (at $k = 0.1$ $\text{h} \, \text{Mpc}^{-1} $) reflecting the
limiting effect of the LLSs on the growth of ionized patches. The statistical
observables such as the RMS of the brightness temperature fluctuations and the
peak amplitudes of the 21-cm power spectra at large-scales ($k = 0.05 - 0.1$
$\text{h} \, \text{Mpc}^{-1} $) are diminished by the presence of LLS. | Host galaxy morphologies of X-ray selected AGN: assessing the
significance of different black hole fueling mechanisms to the accretion
density of the Universe at z~1: We use morphological information of X-ray selected AGN hosts to set limits on
the fraction of the accretion density of the Universe at z~1 that is not likely
to be associated with major mergers. Deep X-ray observations are combined with
high resolution optical data from the Hubble Space Telescope in the AEGIS,
GOODS North and GOODS South fields to explore the morphological breakdown of
X-ray sources in the redshift interval 0.5<z<1.3. The sample is split into
disks, early-type bulge dominated galaxies, peculiar systems and point-sources
in which the nuclear source outshines the host galaxy. The X-ray luminosity
function and luminosity density of AGN at z~1 are then calculated as a function
of morphological type. We find that disk-dominated hosts contribute 30\pm9 per
cent to the total AGN space density and 23\pm6 per cent to the luminosity
density at z~1. We argue that AGN in disk galaxies are most likely fueled not
by major merger events but by minor interactions or internal instabilities. We
find evidence that these mechanisms may be more efficient in producing luminous
AGN (L_X>1e44 erg/s) compared to predictions for the stochastic fueling of
massive black holes in disk galaxies. |
Probing early structure and model-independent neutrino mass with
high-redshift CMB lensing mass maps: CMB lensing maps probe the mass distribution in projection out to high
redshifts, but significant sensitivity to low-redshift structure remains. In
this paper we discuss a method to remove the low-redshift contributions from
CMB lensing mass maps by subtracting suitably scaled galaxy density maps,
nulling the low redshift structure with a model-insensitive procedure that is
similar to delensing. This results in a high-$z$-only mass map that can provide
a probe of structure growth at uniquely high redshifts: if systematics can be
controlled, we forecast that CMB-S4 lensing combined with a Rubin-LSST-like
galaxy survey can probe the amplitude of structure at redshifts $z>3.75$
($z>5$) to within $2.3\%$ ($3.3\%$). We then discuss other example applications
of such high-$z$ CMB lensing maps. In standard analyses of CMB lensing,
assuming the wrong dark energy model (or wrong model parametrization) can lead
to biases in neutrino mass constraints. In contrast, we show with forecasts
that a high-$z$ mass map constructed from CMB-S4 lensing and LSST galaxies can
provide a nearly model-independent neutrino mass constraint, with only
negligible sensitivity to the presence of non-standard dark energy models,
irrespective of their parametrization. | Bayesian model comparison in cosmology with Population Monte Carlo: We use Bayesian model selection techniques to test extensions of the standard
flat LambdaCDM paradigm. Dark-energy and curvature scenarios, and primordial
perturbation models are considered. To that end, we calculate the Bayesian
evidence in favour of each model using Population Monte Carlo (PMC), a new
adaptive sampling technique which was recently applied in a cosmological
context. The Bayesian evidence is immediately available from the PMC sample
used for parameter estimation without further computational effort, and it
comes with an associated error evaluation. Besides, it provides an unbiased
estimator of the evidence after any fixed number of iterations and it is
naturally parallelizable, in contrast with MCMC and nested sampling methods. By
comparison with analytical predictions for simulated data, we show that our
results obtained with PMC are reliable and robust. The variability in the
evidence evaluation and the stability for various cases are estimated both from
simulations and from data. For the cases we consider, the log-evidence is
calculated with a precision of better than 0.08.
Using a combined set of recent CMB, SNIa and BAO data, we find inconclusive
evidence between flat LambdaCDM and simple dark-energy models. A curved
Universe is moderately to strongly disfavoured with respect to a flat
cosmology. Using physically well-motivated priors within the slow-roll
approximation of inflation, we find a weak preference for a running spectral
index. A Harrison-Zel'dovich spectrum is weakly disfavoured. With the current
data, tensor modes are not detected; the large prior volume on the
tensor-to-scalar ratio r results in moderate evidence in favour of r=0.
[Abridged] |
Impact of a Rapid Diluted Energy Density on the halo mass function: We study dark energy cosmological models, extensions of the standard model of
particles, characterized by having an extra relativistic energy density at very
early times, and that rapidly dilute after a phase transition occurs. These
models generate well localized features (or bumps) in the matter power spectrum
for modes crossing the horizon around and before the phase transition epoch.
This is because the presence of the additional energy component enhances the
growth of matter fluctuations during the radiation dominated epoch. Instead of
considering a particular model, we focus on a parametric family of Gaussian
bumps in the matter power spectrum, which otherwise would be a $\Lambda$CDM
one. We study the evolution of such bump cosmologies and their effects in the
halo mass function and halo power spectrum using N-body simulations, the
halo-model based HMcode method, and the peak background split framework. The
bumps are subject to different nonlinear effects that become physically well
understood, and from them we are able to predict that the most distinctive
features will show up for intermediate halo masses $10^{12.3} \,h^{-1}M_{\odot}
< M < 10^{13.6} \,h^{-1}M_{\odot}$. Out of this range, we expect halos are not
significantly affected regardless of the location of the primordial bump in the
matter power spectrum. Our analytical results are accurate and in very
satisfactory agreement with the simulated data. | Mock galaxy shape catalogs in the Subaru Hyper Suprime-Cam Survey: We use the full-sky ray-tracing weak lensing simulations to generate 2268
mock catalogues for the Subaru Hyper Suprime-Cam (HSC) survey first-year shear
catalogue. Our mock catalogues take into account various effects as in the real
data: the survey footprints, inhomogeneous angular distribution of source
galaxies, statistical uncertainties in photometric redshift (photo-$z$)
estimate, variations in the lensing weight, and the statistical noise in galaxy
shape measurements including both intrinsic shapes and the measurement errors.
We then utilize our mock catalogues to evaluate statistical uncertainties
expected in measurements of cosmic shear two-point correlations $\xi_{\pm}$
with tomographic redshift information for the HSC survey. We develop a
quasi-analytical formula for the Gaussian sample variance properly taking into
account the number of source pairs in the survey footprints. The standard
Gaussian formula significantly overestimates or underestimates the mock results
by $50\%$ level. We also show that different photo-$z$ catalogues or the six
disconnected fields, rather than a consecutive geometry, cause variations in
the covariance by $\sim 5\%$. The mock catalogues enable us to study the
chi-square distribution for $\xi_{\pm}$. We find the wider distribution than
that naively expected for the distribution with the degrees-of-freedom of data
vector used. Finally, we propose a method to include non-zero multiplicative
bias in mock shape catalogue and show the non-zero multiplicative bias can
change the effective shape noise in cosmic shear analyses. Our results suggest
an importance of estimating an accurate form of the likelihood function (and
therefore the covariance) for robust cosmological parameter inference from the
precise measurements. |
Cosmology on all scales: a two-parameter perturbation expansion: We propose and construct a two-parameter perturbative expansion around a
Friedmann-Lema\^{i}tre-Robertson-Walker geometry that can be used to model
high-order gravitational effects in the presence of non-linear structure. This
framework reduces to the weak-field and slow-motion post-Newtonian treatment of
gravity in the appropriate limits, but also includes the low-amplitude
large-scale fluctuations that are important for cosmological modelling. We
derive a set of field equations that can be applied to the late Universe, where
non-linear structure exists on supercluster scales, and perform a detailed
investigation of the associated gauge problem. This allows us to identify a
consistent set of perturbed quantities in both the gravitational and matter
sectors, and to construct a set of gauge-invariant quantities that correspond
to each of them. The field equations, written in terms of these quantities,
take on a relatively simple form, and allow the effects of small-scale
structure on the large-scale properties of the Universe to be clearly
identified. We find that inhomogeneous structures source the global expansion,
that there exist new field equations at new orders, and that there is vector
gravitational potential that is a hundred times larger than one might naively
expect from cosmological perturbation theory. Finally, we expect our formalism
to be of use for calculating relativistic effects in upcoming ultra-large-scale
surveys, as the form of the gravitational coupling between small and large
scales depends on the non-linearity of Einstein's equations, and occurs at what
is normally thought of as first order in cosmological perturbations. | Primordial Black Holes as Dark Matter: Almost All or Almost Nothing: Primordial black holes (PBHs) are expected to accrete particle dark matter
around them to form ultracompact minihalos (UCMHs), if the PBHs themselves are
not most of the dark matter. We show that if most dark matter is a thermal
relic, then the inner regions of UCMHs around PBHs are highly luminous sources
of annihilation products. Flux constraints on gamma rays and neutrinos set
strong abundance limits, improving previous limits by orders of magnitude.
Assuming enough particle dark matter exists to form UCMHs, we find that
Omega_PBH <~ 10^-4 (for m_DM c^2 ~ 100 GeV) for a vast range in PBH mass. We
briefly discuss the uncertainties on our limits, including those due to the
evolution of the UCMH luminosity as it annihilates. |
Evidence for a receding dust sublimation region around a supermassive
black hole: The near-IR emission in Type 1 AGNs is thought to be dominated by the thermal
radiation from dust grains that are heated by the central engine in the
UV/optical and are almost at the sublimation temperature. A brightening of the
central source can thus further sublimate the innermost dust, leading to an
increase in the radius of the near-IR emitting region. Such changes in radius
have been indirectly probed by the measurements of the changes in the time lag
between the near-IR and UV/optical light variation. Here we report direct
evidence for such a receding sublimation region through the near-IR
interferometry of the brightest Type 1 AGN in NGC4151. The increase in radius
follows a significant brightening of the central engine with a delay of at
least a few years, which is thus the implied destruction timescale of the
innermost dust distribution. Compiling historic flux variations and radius
measurements, we also infer the reformation timescale for the inner dust
distribution to be several years in this galactic nucleus. More specifically
and quantitatively, we find that the radius at a given time seems to be
correlated with a long-term average of the flux over the previous several (~6)
years, instead of the instantaneous flux. Finally, we also report measurements
of three more Type 1 AGNs newly observed with the Keck interferometer, as well
as the second epoch measurements for three other AGNs. | A model independent null test on the cosmological constant: We use the Om statistic and the Genetic Algorithms (GA) in order to derive a
null test on the spatially flat cosmological constant model $\Lambda$CDM. This
is done in two steps: first, we apply the GA to the Constitution SNIa data in
order to acquire a model independent reconstruction of the expansion history of
the Universe $H(z)$ and second, we use the reconstructed $H(z)$ in conjunction
with the Om statistic, which is constant only for the $\Lambda$CDM model, to
derive our constraints. We find that while $\Lambda$CDM is consistent with the
data at the $2\sigma$ level, some deviations from $\Lambda$CDM model at low
redshifts can be accommodated. |
On the Time Variation of Dust Extinction and Gas Absorption for Type~Ia
Supernovae Observed Through Non-uniform Interstellar Medium: For Type Ia supernovae (SNe Ia) observed through a non-uniform interstellar
medium (ISM) in its host galaxy, we investigate whether the non-uniformity can
cause observable time variations in dust extinction and in gas absorption due
to the expansion of the SN photosphere with time. We show that, owing to the
steep spectral index of the ISM density power spectrum, sizable density
fluctuation amplitudes at the length scale of typical ISM structures ($\gtrsim
\text{ 10 pc}$) will translate to much smaller fluctuations on the scales of a
SN photosphere. Therefore the typical amplitude of time variation due to
non-uniform ISM, of absorption equivalent widths and of extinction, would be
small. As a result, we conclude that non-uniform ISM density should not impact
cosmology measurements based on SNe Ia. We apply our predictions based on the
ISM density power law power spectrum to the observations of two highly reddened
SNe Ia, SN 2012cu and SN 2014J. | Cosmological Constraints from the Anisotropic Clustering Analysis using
BOSS DR9: Our observations of the Universe are fundamentally anisotropic, with data
from galaxies separated transverse to the line of sight coming from the same
epoch while that from galaxies separated parallel to the line of sight coming
from different times. Moreover, galaxy velocities along the line of sight
change their redshift, giving redshift space distortions. We perform a full
two-dimensional anisotropy analysis of galaxy clustering data, fitting in a
substantially model independent manner the angular diameter distance D_A,
Hubble parameter H, and growth rate ddelta/dln a without assuming a dark energy
model. The results demonstrate consistency with LCDM expansion and growth,
hence also testing general relativity. We also point out the interpretation
dependence of the effective redshift z_eff, and its cosmological impact for
next generation surveys. |
Constraining Cosmological Parameters using the Cluster Mass-Richness
Relation: The cluster mass-richness relation (MRR) is an observationally efficient and
potentially powerful cosmological tool for constraining the mean matter density
of the universe and the amplitude of fluctuations using the cluster abundance
technique. We derive the MRR relation using GalWCat19, a publicly available
galaxy cluster catalog we created from the Sloan Digital Sky Survey-DR13
spectroscopic dataset. The MRR shows a tail at the low-richness end. Using the
Illustris-TNG and mini-Uchuu cosmological numerical simulations, we demonstrate
that this tail is caused by systematical uncertainties. We show that, by means
of a judicious cut, identified by the use of the Hinge function, it is possible
to determine a richness threshold above which the MRR is linear i.e., where
cluster mass scales with richness as logM_200 = alpha + beta logN_200. We
derive the MRR and show it is consistent with both sets of simulations with a
slope of beta ~ 1. We use our MRR to estimate cluster masses from the GalWCat19
catalog which we then use to set constraints on omega_m and sigma_8. Utilizing
the all-member MRR, we obtain constraints of omega_m = 0.31 (+0.04-0.03) and
sigma_8 = 0.82 (+0.05-0.04), and utilizing the red-member MRR, we obtain
omega_m = 0.31 (+0.04-0.03) and sigma_8 = 0.81 (+0.05-0.04). Our constraints on
omega_m and sigma_8 are consistent and very competitive with the Planck 2018
results. | New highly precise weak gravitational lensing flexions measurement
method based on ERA method: Weak gravitational lensing flexions are a kind of weak lensing distortion
which are defined as the spin 1 and spin 3 combinations of the third order
derivatives of gravitational lensing potential. Since the shear has spin 2
combination of the second order derivative, the flexion signal gives a partly
independent information from shear signal and is more sensitive to the local
mass distribution than shear signal. Thus its measurement is expected to play
important roles in observational cosmology. However, since the weakness of the
flexion signal as well as the complicatedness of its intrinsic noise made its
accurate observation very difficult. We propose a new method of measuring the
flexion signal using ERA method which is a method to measure weak lensing shear
without any approximation. We find two particular combinations of the flexions
which provide the quantities with only lensing information and free of
intrinsic noise when taken average. It is confirmed by simple numerical
simulation that the statistical average of these combinations do not in fact
depend on the strength of the intrinsic distortion. |
Measurement and Calibration of Noise Bias in Weak Lensing Galaxy Shape
Estimation: Weak gravitational lensing has the potential to constrain cosmological
parameters to high precision. However, as shown by the Shear TEsting Programmes
(STEP) and GRavitational lEnsing Accuracy Testing (GREAT) Challenges, measuring
galaxy shears is a nontrivial task: various methods introduce different
systematic biases which have to be accounted for. We investigate how pixel
noise on the image affects the bias on shear estimates from a
Maximum-Likelihood forward model-fitting approach using a sum of co-elliptical
S\'{e}rsic profiles, in complement to the theoretical approach of an an
associated paper. We evaluate the bias using a simple but realistic galaxy
model and find that the effects of noise alone can cause biases of order 1-10%
on measured shears, which is significant for current and future lensing
surveys. We evaluate a simulation-based calibration method to create a bias
model as a function of galaxy properties and observing conditions. This model
is then used to correct the simulated measurements. We demonstrate that this
method can effectively reduce noise bias so that shear measurement reaches the
level of accuracy required for estimating cosmic shear in upcoming lensing
surveys. | Residual Hubble-bubble effects on supernova cosmology: Even in a universe that is homogeneous on large scales, local density
fluctuations can imprint a systematic signature on the cosmological inferences
we make from distant sources. One example is the effect of a local
under-density on supernova cosmology. Also known as a Hubble-bubble, it has
been suggested that a large enough under-density could account for the
supernova magnitude- redshift relation without the need for dark energy or
acceleration. Although the size and depth of under-density required for such an
extreme result is extremely unlikely to be a random fluctuation in an
on-average homogeneous universe, even a small under-density can leave residual
effects on our cosmological inferences.
In this paper we show that there remain systematic shifts in our cosmological
parameter measure- ments, even after excluding local supernovae that are likely
to be within any small Hubble-bubble. We study theoretically the low-redshift
cutoff typically imposed by supernova cosmology analyses, and show that a
low-redshift cut of z0 \sim 0.02 may be too low based on the observed
inhomogeneity in our local universe.
Neglecting to impose any low-redshift cutoff can have a significant effect on
the cosmological pa- rameters derived from supernova data. A slight local
under-density, just 30% under-dense with scale 70h^{-1} Mpc, causes an error in
the inferred cosmological constant density {\Omega}{\Lambda} of \sim 4%.
Imposing a low-redshift cutoff reduces this systematic error but does not
remove it entirely. A residual systematic shift of 0.99% remains in the
inferred value {\Omega}{\Lambda} even when neglecting all data within the
currently pre- ferred low-redshift cutoff of 0.02. Given current measurement
uncertainties this shift is not negligible, and will need to be accounted for
when future measurements yield higher precision. |
The ALHAMBRA survey: an empirical estimation of the cosmic variance for
merger fraction studies based on close pairs: Our goal is to estimate empirically, for the first time, the cosmic variance
that affects merger fraction studies based on close pairs. We compute the
merger fraction from photometric redshift close pairs with 10h^-1 kpc <= rp <=
50h^-1 kpc and Dv <= 500 km/s, and measure it in the 48 sub-fields of the
ALHAMBRA survey. We study the distribution of the measured merger fractions,
that follow a log-normal function, and estimate the cosmic variance sigma_v as
the intrinsic dispersion of the observed distribution. We develop a maximum
likelihood estimator to measure a reliable sigma_v and avoid the dispersion due
to the observational errors (including the Poisson shot noise term). The cosmic
variance of the merger fraction depends mainly on (i) the number density of the
populations under study, both for the principal (n_1) and the companion (n_2)
galaxy in the close pair, and (ii) the probed cosmic volume V_c. We find a
significant dependence on neither the search radius used to define close
companions, the redshift, nor the physical selection (luminosity or stellar
mass) of the samples. We provide a parametrisation of the cosmic variance with
n_1, n_2, and V_c, sigma_v = 0.48 n_1^{-0.54} V_c^{-0.48} (n_2/n_1)^{-0.37}.
Thanks to this prescription, future merger fraction studies based on close
pairs could account properly for the cosmic variance on their results. | WMAP Constraints On K-Inflation: We study the K-Inflation models where the inflaton field has non-canonical
kinetic term. In particular, we consider the Dirac-Born-Infeld (DBI) form for
the kinetic energy of the inflaton field. We consider quadratic and quartic
potentials as well as the potential for the natural inflation. We use a
modified version of the MODECODE (proposed by Mortonson et al.) to calculate
the power spectrum of the primordial perturbations generated by the inflaton
field and subsequently use the WMAP7 results to constrain the models.
Interestingly with DBI type kinetic term, lesser gravity waves are produced as
one approaches more towards scale invariance. This is true for all the
potentials considered. Unlike the canonical case, this feature, in particular,
helps the quartic ($\lambda\phi^4$) potential with DBI type kinetic term to be
consistent with WMAP data. |
Constraining the growth rate on linear scales by combining SKAO and DESI
surveys: In the pursuit of understanding the large-scale structure of the Universe,
the synergy between complementary cosmological surveys has proven to be a
powerful tool. Using multiple tracers of the large-scale structure can
significantly improve the constraints on cosmological parameters. We explore
the potential of combining the Square Kilometre Array Observatory (SKAO) and
the Dark Energy Spectroscopic Instrument (DESI) spectroscopic surveys to
enhance precision on the growth rate of cosmic structures. We employ a
multitracer Fisher analysis to estimate precision on the growth rate when using
pairs of mock surveys that are based on SKAO and DESI specifications. The pairs
are at both low and high redshifts. For SKA-MID, we use the HI galaxy and the
HI intensity mapping samples. In order to avoid the complexities and
uncertainties at small scales, we confine the analysis to scales where linear
perturbations are reliable. The consequent loss of signal in each individual
survey is mitigated by the gains from the multi-tracer. After marginalising
over cosmological and nuisance parameters, we find a significant improvement in
the precision on the growth rate. | A foreground-marginalized 'BK-lite' likelihood for the tensor-to-scalar
ratio: The current limit on the tensor-to-scalar ratio from the BICEP/Keck
Collaboration (with r<0.036 at 95% confidence) puts pressure on early universe
models, with less than 10% of the error on r attributed to uncertainty in
Galactic foregrounds. We use the BICEP/Keck BK18 public multi-frequency
likelihood to test some further assumptions made in the foreground modeling,
finding little impact on the estimate for r. We then estimate
foreground-marginalized cosmic microwave background (CMB) B-mode polarization
bandpowers. We fit them with a multivariate offset-lognormal distribution and
construct a marginalized 'BK-lite' likelihood for the CMB B-mode spectrum with
no nuisance parameters, serving as a method demonstration for future analyses
of small sky regions, for example from the South Pole Observatory or CMB-S4. |
Cosmic voids uncovered -- first-order statistics of depressions in the
biased density field: Cosmic voids are the major volume component in the matter distribution of the
Universe. They posses great potential for constraining dark energy as well as
for testing theories of gravity. Nevertheless, in spite of their growing
popularity as cosmological probes, a gap of knowledge between cosmic void
observations and theory still persists. In particular, the void size function
models proposed in literature have been proven unsuccessful in reproducing the
results obtained from cosmological simulations in which cosmic voids are
detected from biased tracers of the density field, undermining the possibility
of using them as cosmological probes. The goal of this work is to cover this
gap. In particular, we make use of the findings of a previous work in which we
have improved the void selection procedure, presenting an algorithm that
redefines the void ridges and, consequently, their radius. By applying this
algorithm, we validate the volume conserving model of the void size function on
a set of unbiased simulated density field tracers. We highlight the difference
in the internal structure between voids selected in this way and those
identified by the popular VIDE void finder. We also extend the validation of
the model to the case of biased tracers. We find that a relation exists between
the tracer used to sample the underlying dark matter density field and its
unbiased counterpart. Moreover, we demonstrate that, as long as this relation
is accounted for, the size function is a viable approach for studying cosmology
with cosmic voids. | Can we distinguish the adiabatic fluctuations and isocurvature
fluctuations with pulsar timing arrays?: Understanding the nature of primordial fluctuations is critical to our
comprehension of the Universe's early stages. While these fluctuations are
known to be nearly scale-invariant, quasi-adiabatic, and nearly Gaussian on
large scales, their behavior at smaller scales remains less well-defined and
may offer insights into new physics. Recent observations by the NANOGrav, PPTA,
EPTA, and CPTA collaborations suggest the presence of a stochastic
gravitational wave background, which, while consistent with the contribution
from supermassive black hole binaries, also opens the possibility of probing
new physics. This paper explores whether this signal could stem from primordial
isocurvature and adiabatic fluctuations. We adopt parameterized spectra for
both types of fluctuations to fit the observations from the latest NANOGrav
data. Furthermore, we employ Bayesian analysis to assess the distinguishability
of these models in light of current PTA sensitivities. Our findings indicate
that with the capabilities, PTAs cannot conclusively differentiate between
isocurvature and adiabatic fluctuations. |
Observatons of NGC 3077 Galaxy in Narrow Band [SII] and H_alpha Filters: We present observations of the HI tidal arm near dwarf galaxy NGC 3077
(member of the M81 galaxy group) in narrow band [SII] and H_alpha filters.
Observations were carried out in March 2011 with the 2m RCC telescope at NAO
Rozhen, Bulgaria. Our search for possible supernova remnant candidates
(identified as sources with enhanced [SII] emission relative to their H_alpha
emission) in this region yielded no sources of this kind. Nevertheless, we
found a number of objects with significant H_alpha emission that probably
represent uncatalogued, low brightness HII regions. | Local observer effect on the cosmological soft theorem: Non-Gaussianities of primordial perturbations in the soft limit provide the
important information about the light degrees of freedom during inflation. The
soft modes of the curvature perturbations, unobservable for a local observer,
act as rescaling the spatial coordinates. We determine how the trispectrum in
the collapsed limit is shifted by the rescaling due to the soft modes. We find
the form of the inequality between $f_{\rm NL}$ and $\tau_{\rm NL}$ parameters
is not affected by the rescaling, demonstrating that the role of the inequality
as an indicator of the light degrees of freedom remains intact. We also comment
on the local observer effect on the consistency relation for ultra slow-roll
inflation. |
Radially extended kinematics and stellar populations of the massive
ellipticals NGC1600, NGC4125 and NGC7619. Constraints on the outer dark halo
density profile: We present high quality long slit spectra along the major and minor axes out
to 1.5-2 Re (14-22 kpc) of three bright elliptical galaxies (NGC1600, NGC4125,
NGC7619) obtained at the Hobby-Eberly Telescope (HET). We derive stellar
kinematic profiles and Lick/IDS indices (Hbeta, Mgb, Fe5015, Fe5270, Fe5335,
Fe5406). Moreover, for NGC4125 we derive gas kinematics and emission line
strengths. We model the absorption line strengths using Simple Stellar
Populations models that take into account the variation of [\alpha/Fe] and
derive ages, total metallicity and element abundances. Overall, we find that
the three galaxies have old and [\alpha/Fe] overabundant stellar populations
with no significant gradients. The metallicity is supersolar at the center with
a strong negative radial gradient. For NGC4125, several pieces of evidence
point to a recent dissipational merger event. We calculate the broad band color
profiles with the help of SSP models. All of the colors show sharp peaks at the
center of the galaxies, mainly caused by the metallicity gradients, and agree
well with the measured colors. Using the Schwarzschild's axisymmetric orbit
superposition technique, we model the stellar kinematics to constrain the dark
halos of the galaxies. We use the tight correlation between the Mgb strength
and local escape velocity to set limits on the extent of the halos by testing
different halo sizes. Logarithmic halos - cut at 60 kpc -minimize the overall
scatter of the Mgb-Vesc relation. Larger cutoff radii are found if the dark
matter density profile is decreasing more steeply at large radii. | Cosmology With Low-Redshift Observations: No Signal For New Physics: We analyse various low-redshift cosmological data from Type-Ia Supernova,
Baryon Acoustic Oscillations, Time-Delay measurements using Strong-Lensing,
$H(z)$ measurements using Cosmic Chronometers and growth measurements from
large scale structure observations for $\Lambda$CDM and some different dark
energy models. By calculating the Bayesian Evidence for different dark energy
models, we find out that the $\Lambda$CDM still gives the best fit to the data
with $H_{0}=70.3^{+1.36}_{-1.35}$ Km/s/Mpc (at $1\sigma$). This value is in
$2\sigma$ or less tension with various low and high redshift measurements for
$H_{0}$ including SH0ES, Planck-2018 and the recent results from H0LiCOW-XIII.
The derived constraint on $S_{8}=\sigma_{8}\sqrt{{\Omega_{m0}}/{0.3}}$ from our
analysis is $S_{8} = 0.76^{+0.03}_{-0.03}$, fully consistent with direct
measurement of $S_{8}$ by KiDS+VIKING-450+DES1 survey. We hence conclude that
the $\Lambda$CDM model with parameter constraints obtained in this work is
consistent with different early and late Universe observations within
$2\sigma$. We therefore, do not find any compelling reason to go beyond
concordance $\Lambda$CDM model. |
Sensitivity of gamma-ray telescopes for detection of magnetic fields in
intergalactic medium: We explore potential of current and next-generation gamma-ray telescopes for
the detection of weak magnetic fields in the intergalactic medium. We
demonstrate that using two complementary techniques, observation of extended
emission around point sources and observation of time delays in gamma-ray
flares, one would be able to probe most of the cosmologically and
astrophysically interesting part of the "magnetic field strength" vs.
"correlation length" parameter space. This implies that gamma-ray observations
with Fermi and ground-based Cherenkov telescopes will allow to (a) strongly
constrain theories of the origin of magnetic fields in galaxies and galaxy
clusters and (b) discover, constrain or rule out the existence of weak
primordial magnetic field generated at different stages of evolution of the
Early Universe. | On the validity of the Born approximation for weak cosmic flexions: Weak lensing calculations are often made under the assumption of the Born
approximation, where the ray path is approximated as a straight radial line. In
addition, lens-lens couplings where there are several deflections along the
light ray are often neglected. We examine the effect of dropping the Born
approximation and taking lens-lens couplings into account, for weak lensing
effects up to second order (cosmic flexion), by making a perturbative expansion
in the light path. We present a diagrammatic representation of the resulting
corrections to the lensing effects. The flexion signal, which measures the
derivative of the density field, acquires correction terms proportional to the
squared gravitational shear; we also find that by dropping the Born
approximation, two further degrees of freedom of the lensing distortion can be
excited (the twist components), in addition to the four standard flexion
components. We derive angular power spectra of the flexion and twist, with and
without the Born-approximation and lens-lens couplings and confirm that the
Born approximation is an excellent approximation for weak cosmic flexions,
except at very small scales. |
BeyondPlanck III. Commander3: We describe the computational infrastructure for end-to-end Bayesian CMB
analysis implemented by the BeyondPlanck collaboration. This code is called
commander3, and provides a statistically consistent framework for global
analysis of CMB and microwave observations, and may be useful for a wide range
of legacy, current, and future experiments. The paper has three main goals.
Firstly, we provide a high-level overview of the existing code base, aiming to
guide readers who wish to extend and adapt the code according to their own
needs, or to reimplement it from scratch in a different programming language.
Secondly, we discuss some critical computational challenges that arise within
any global CMB analysis framework, for instance in-memory compression of
time-ordered data, FFT optimization, and parallelization and load-balancing.
Thirdly, we quantify the CPU and RAM requirements for the current BeyondPlanck
analysis, and find that a total of 1.5 TB of RAM is required for efficient
analysis, and the total cost of a full Gibbs sample is 170 CPU-hrs, including
both low-level processing and high-level component separation, which is well
within the capabilities of current low-cost computing facilities. The existing
code base is made publicly available under a GNU General Public Library (GPL)
license. | Early dark energy resolution to the Hubble tension in light of weak
lensing surveys and lensing anomalies: Early Dark Energy (EDE) contributing a fraction $f_{\rm EDE}(z_c)\sim 10 \%$
of the energy density of the universe around $z_c\simeq 3500$ and diluting as
or faster than radiation afterwards, can provide a resolution to the Hubble
tension, the $\sim 5\sigma$ discrepancy between the $H_0$ value derived from
early- and late-universe observations within $\Lambda$CDM. However, it has been
pointed out that Large-Scale Structure (LSS) data, which are in $\sim3\sigma$
tension with $\Lambda$CDM and EDE cosmologies, might alter these conclusions.
We reassess the viability of the EDE against a host of high- and low-redshift
measurements, by combining LSS observations from recent weak lensing (WL)
surveys with CMB, Baryon Acoustic Oscillation (BAO), growth function (FS) and
Supernova Ia (SNIa) data. Introducing a model whose only parameter is $f_{\rm
EDE}(z_c)$, we report a $\sim 2\sigma$ preference for non-zero $f_{\rm
EDE}(z_c)$ from Planck data alone and the tension with SH0ES is reduced below
$2\sigma$. Adding BAO, FS and SNIa does not affect this result, while the
inclusion of a prior on $H_0$ from SH0ES increase the preference for non-zero
EDE to $\sim3.6\sigma$. After checking the EDE non-linear matter power spectrum
predicted by standard semi-analytical algorithms via a set of $N$-body
simulations, we show that current WL data do not rule out EDE. We also caution
against the interpretation of constraints obtained from combining statistically
inconsistent data sets within the $\Lambda$CDM cosmology. In light of the CMB
lensing anomalies, we show that the lensing-marginalized CMB data also favor
non-zero $f_{\rm EDE}(z_c)$ at $\sim2\sigma$, predicts $H_0$ in $1.4\sigma$
agreement with SH0ES and $S_8$ in $1.5\sigma$ ($0.8\sigma$) agreement with KV
(DES) data. Alternatively, we discuss promising extensions of the EDE cosmology
that could allow to fully restore cosmological concordance. |
A coordinate-independent technique for detecting globally inhomogeneous
flat topologies: A flat Universe model supported by recent observations has 18 possible
choices for its overall topology. To detect or exclude these possibilities is
one of the most important tasks in modern cosmology, but it has been very
difficult for globally inhomogeneous ones because of a long-time calculation.
In this brief paper we provide an object-based 3D method to overcome the
problem, as an extension of Fujii & Yoshii (2011a). Though the test depends on
the observer's location in the universe, this method drastically reduces
calculation times to constrain inhomogeneous topologies, and will be useful in
exhaustively constraining the size of the Universe. | Assembly Bias of Dwarf-sized Dark Matter Haloes: Previous studies indicate that assembly bias effects are stronger for lower
mass dark matter haloes. Here we make use of high resolution re-simulations of
rich clusters and their surroundings from the Phoenix Project and a large
volume cosmological simulation, the Millennium-II run, to quantify assembly
bias effects on dwarf-sized dark matter haloes. We find that, in the regions
around massive clusters, dwarf-sized haloes ($[10^9,10^{11}]\ms$) form earlier
($\Delta z \sim 2$ in redshift) and possess larger $V_{\rm max}$ ($\sim20%$)
than the field galaxies. We find that this environmental dependence is largely
caused by tidal interactions between the ejected haloes and their former hosts,
while other large scale effects are less important. Finally we assess the
effects of assembly bias on dwarf galaxy formation with a sophisticated
semi-analytical galaxy formation model. We find that the dwarf galaxies near
massive clusters tend to be redder ($\Delta(u-r) = 0.5$) and have three times
as much stellar mass compared to the field galaxies with the same halo mass.
These features should be seen with observational data. |
Accurately simulating anisotropic thermal conduction on a moving mesh: We present a novel implementation of an extremum preserving anisotropic
diffusion solver for thermal conduction on the unstructured moving Voronoi mesh
of the AREPO code. The method relies on splitting the one-sided facet fluxes
into normal and oblique components, with the oblique fluxes being limited such
that the total flux is both locally conservative and extremum preserving. The
approach makes use of harmonic averaging points and a simple, robust
interpolation scheme that works well for strong heterogeneous and anisotropic
diffusion problems. Moreover, the required discretisation stencil is small.
Efficient fully implicit and semi-implicit time integration schemes are also
implemented. We perform several numerical tests that evaluate the stability and
accuracy of the scheme, including applications such as point explosions with
heat conduction and calculations of convective instabilities in conducting
plasmas. The new implementation is suitable for studying important
astrophysical phenomena, such as the conductive heat transport in galaxy
clusters, the evolution of supernova remnants, or the distribution of heat from
blackhole-driven jets into the intracluster medium. | CARMA observations of massive Planck-discovered cluster candidates at
z>0.5 associated with WISE overdensities: Breaking the size-flux degeneracy: We use a Bayesian software package to analyze CARMA-8 data towards 19
unconfirmed Planck SZ-cluster candidates from Rodriguez-Gonzalvez et al.
(2015), that are associated with significant overdensities in WISE. We used two
cluster parameterizations, one based on a (fixed shape) generalized-NFW
pressure profile and another based on a beta-gas-density profile (with varying
shape parameters) to obtain parameter estimates for the nine CARMA-8
SZ-detected clusters. We find our sample is comprised of massive,
Y_{500}=0.0010 \pm 0.0015 arcmin^2, relatively compact, theta_{500}= 3.9 \pm
2.0 arcmin systems. Results from the beta model show that our cluster
candidates exhibit a heterogeneous set of brightness-temperature profiles.
Comparison of Planck and CARMA-8 measurements showed good agreement in Y_{500}
and an absence of obvious biases. We estimated the total cluster mass M_{500}
as a function of z for one of the systems; at the preferred photometric
redshift of 0.5, the derived mass, M_{500} \approx 0.8 \pm 0.2 \times 10^{15}
Msun. Spectroscopic Keck/MOSFIRE data confirmed a galaxy member of one of our
cluster candidates to be at z=0.565. Applying a Planck prior in Y_{500} to the
CARMA-8 results reduces uncertainties for both parameters by a factor >4,
relative to the independent Planck or CARMA-8 measurements. We here demonstrate
a powerful technique to find massive clusters at intermediate z \gtrsim 0.5
redshifts using a cross-correlation between Planck and WISE data, with
high-resolution follow-up with CARMA-8. We also use the combined capabilities
of Planck and CARMA-8 to obtain a dramatic reduction by a factor of several, in
parameter uncertainties. |
Star Clusters in M31: Old Clusters with Bar Kinematics: We analyze our accurate kinematical data for the old clusters in the inner
regions of M31. These velocities are based on high S/N Hectospec data (Caldwell
et al 2010). The data are well suited for analysis of M31's inner regions
because we took particular care to correct for contamination by unresolved
field stars from the disk and bulge in the fibers. The metal poor clusters show
kinematics which are compatible with a pressure-supported spheroid. The
kinematics of metal-rich clusters, however, argue for a disk population. In
particular the innermost region (inside 2 kpc) shows the kinematics of the x2
family of bar periodic orbits, arguing for the existence of an inner Lindblad
resonance in M31. | 3D simulations with boosted primordial power spectra and ultracompact
minihalos: We perform three-dimensional simulations of structure formation in the early
Universe, when boosting the primordial power spectrum on approximately kpc
scales. We demonstrate that our simulations are capable of producing power-law
profiles close to the steep $\rho\propto r^{-9/4}$ halo profiles that are
commonly assumed to be a good approximation to ultracompact minihalos (UCMHs).
However, we show that for more realistic initial conditions in which halos are
neither perfectly symmetric nor isolated, the steep power-law profile is
disrupted and we find that the Navarro-Frenk-White profile is a better fit to
most halos. In the presence of background fluctuations even extreme, nearly
spherical initial conditions do not remain exceptional. Nonetheless, boosting
the amplitude of initial fluctuations causes all structures to form earlier and
thus at larger densities. With sufficiently large amplitude of fluctuations we
find that values for the concentration of typical halos in our simulations can
become very large. However, despite the signal coming from dark matter
annihilation inside the cores of these halos being enhanced, it is still
orders-of-magnitude smaller compared to the usually assumed UCMH profile. The
upper bound on the primordial power spectrum from the non-observation of UCMHs
should therefore be re-evaluated. |
SDSS J0025-10 at z=0.30: a (U)LIRG to optical QSO transition candidate: We have characterized the amount, spatial distribution and kinematics of the
molecular gas in the merging, double nucleus type 2 quasar SDSS J0025-10 at
z=0.30 using the CO(1-0) transition, based on data obtained with ATCA. This is
one of the scarce examples of quasar host galaxies where the CO emission has
been resolved spatially at any redshift. We infer a molecular gas mass M(H2) =
(6 +/- 1) x 1e9 Msun, which is distributed in two main reservoirs separated by
~9 kpc. ~60% of the gas is in the central region, associated with the QSO
nucleus and/or the intermediate region between the two nuclei. The other 40% is
associated with the northern tidal tail and is therefore unsettled.
With its high infrared luminosity L(IR) = (1.1 +/- 0.3) x 1e12 Lsun, SDSS
J0025-10 is an analogue of local luminous LIRGs and ULIRGs. On the other hand,
the clear evidence for an ongoing major merger of two gas rich progenitors, the
high L(IR) dominated by a starburst, the massive reservoir of molecular gas
with a large fraction still unsettled, and the quasar activity are all
properties consistent with a transition phase in the (U)LIRG-optical QSO
evolutionary scenario. We propose that we are observing the system during a
particular transient phase, prior to more advanced mergers where the nuclei
have already coalesced.
We argue that a fraction of the molecular gas reservoir is associated with a
tidal dwarf galaxy identified in the optical HST image at the tip of the
northern tidal tail. The formation of such structures is predicted by
simulations of colliding galaxies. | Reconstructing the shape of the correlation function: We develop an estimator for the correlation function which, in the ensemble
average, returns the shape of the correlation function, even for signals that
have significant correlations on the scale of the survey region. Our estimator
is general and works in any number of dimensions. We develop versions of the
estimator for both diffuse and discrete signals. As an application, we examine
Monte Carlo simulations of X-ray background measurements. These include a
realistic, spatially-inhomogeneous population of spurious detector events. We
discuss applying the estimator to the averaging of correlation functions
evaluated on several small fields, and to other cosmological applications. |
A closer look at the cosmological implications of the $Λ$HDE model: In a previous paper, we proposed a heterotic dark energy model, called
$\Lambda$HDE, in which dark energy is composed of two components: cosmological
constant (CC) and holographic dark energy (HDE). The aim of this work is to
give a more comprehensive and systematic investigation on the cosmological
implications of the $\Lambda$HDE model. Firstly, we make use of the current
observations to constrain the $\Lambda$HDE model, and compare its cosmology-fit
results with the results of the $\Lambda$CDM and the HDE model. Then, by
combining a qualitative theoretical analysis with a quantitative numerical
study, we discuss the impact of considering curvature on the cosmic evolutions
of fractional HDE density $\Omega_{hde}$ and fractional CC density
$\Omega_{\Lambda}$, as well as on the ultimate cosmic fate. Finally, we explore
the effects of adopting different types of observational data. We find that:
(1) the current observational data cannot distinguish the $\Lambda$HDE model
from the $\Lambda$CDM and the HDE model; this indicates that DE may contain
multiple components. (2) the asymptotic solution of $\Omega_{hde}$ and the
corresponding cosmic fate in a flat universe can be extended to the case of a
non-flat universe; moreover, compared with the case of a flat universe,
considering curvature will make HDE closer to a phantom dark energy. (3)
compared with JLA dataset, SNLS3 data more favor a phantom type HDE; in
contrast, using other types of observational data have no significant impact on
the cosmic evolutions of the $\Lambda$HDE model. | Multiple Lensing of the Cosmic Microwave Background anisotropies: We study the gravitational lensing effect on the Cosmic Microwave Background
(CMB) anisotropies performing a ray-tracing of the primordial CMB photons
through intervening large-scale structures (LSS) distribution predicted by
N-Body numerical simulations with a particular focus on the precise recovery of
the lens-induced polarized counterpart of the source plane. We apply both a
multiple plane ray-tracing and an effective deflection approach based on the
Born approximation to deflect the CMB photons trajectories through the
simulated lightcone. We discuss the results obtained with both these methods
together with the impact of LSS non-linear evolution on the CMB temperature and
polarization power spectra. We compare our results with semi-analytical
approximations implemented in Boltzmann codes like, e.g., CAMB. We show that,
with our current N-body setup, the predicted lensing power is recovered with
good accuracy in a wide range of multipoles while excess power with respect to
semi-analytic prescriptions is observed in the lensing potential on scales
$\ell \gtrsim 3000$. We quantify the impact of the numerical effects connected
to the resolution in the N-Body simulation together with the resolution and
band-limit chosen to synthesise the CMB source plane. We found these quantities
to be particularly important for the simulation of B-mode polarization power
spectrum. |
An Inpainting Approach to Tackle the Kinematic and Thermal SZ Induced
Biases in CMB-Cluster Lensing Estimators: A galaxy cluster's own Sunyaev-Zel{'}dovich (SZ) signal is known to be a
major contaminant when reconstructing the cluster's underlying lensing
potential using cosmic microwave background (CMB) temperature maps. In this
work, we develop a modified quadratic estimator (QE) that is designed to
mitigate the lensing biases due to the kinematic and thermal SZ effects. The
idea behind the approach is to use inpainting to eliminate the cluster's own
emission from the large-scale CMB gradient map. In this inpainted gradient map,
we fill the pixel values at the cluster location using a constrained Gaussian
realization based on the information from surrounding regions. We show that the
noise induced due to inpainting process is small compared to other noise
sources for upcoming surveys and has minimal impact on the final lensing
signal-to-noise. Without any foreground cleaning, we find a stacked mass
uncertainty of 6.5% for the CMB-S4 experiment on a cluster sample containing
5000 clusters with $M_{200c} = 2 \times 10^{14}\ M_{\odot}$ at z = 0.7. In
addition to the SZ-induced lensing biases, we also quantify the low mass bias
arising due to the contamination of the CMB gradient by the cluster
convergence. For the fiducial cluster sample considered in this work, we find
that bias is negligible compared to the statistical uncertainties for both the
standard and the modified QE even when modes up to $\sim 2700$ are used for the
gradient estimation. With more gradient modes, we demonstrate that the
sensitivity can be increased by 14% compared to the fiducial result above with
gradient modes up to $2000$ | Precise Measurement of the Reionization Optical Depth from The Global
21-cm Signal Accounting for Cosmic Heating: As a result of our limited data on reionization, the total optical depth for
electron scattering, $\tau$, limits precision measurements of cosmological
parameters from the Cosmic Microwave Background (CMB). It was recently shown
that the predicted 21-cm signal of neutral hydrogen contains enough information
to reconstruct $\tau$ with sub-percent accuracy, assuming that the neutral gas
was much hotter than the CMB throughout the entire epoch of reionization. Here
we relax this assumption and use the global 21-cm signal alone to extract
$\tau$ for realistic X-ray heating scenarios. We test our model-independent
approach using mock data for a wide range of ionization and heating histories
and show that an accurate measurement of the reionization optical depth at a
sub-percent level is possible in most of the considered scenarios even when
heating is not saturated during the epoch of reionization, assuming that the
foregrounds are mitigated. However, we find that in cases where heating sources
had hard X-ray spectra and their luminosity was close to or lower than what is
predicted based on low-redshift observations, the global 21-cm signal alone is
not a good tracer of the reionization history. |
Neutrino properties from cosmology: The interplay between cosmology and earth based experiments is crucial in
order to pin down neutrino physics. Indeed cosmology can provide very tight,
yet model dependent, constraints on some neutrino properties. Here we focus on
the neutrino mass sum, reviewing the up to date current bounds and showing the
results of our forecast of the sensitivity of future experiments. Finally, we
discuss the case for sterile neutrinos, explaining how non standard sterile
neutrino self-interactions can reconcile the oscillation anomalies with
cosmology. | Investigating the Core Morphology-Seyfert Class relationship with Hubble
Space Telescope Archival Images of local Seyfert galaxies: The Unified Model of Active Galactic Nuclei (AGN) has provided a successful
explanation for the observed diversity of AGN in the local Universe. However,
recent analysis of multi-wavelength spectral and image data suggests that the
Unified Model is only a partial theory of AGN, and may need to be augmented to
remain consistent with all observations. Recent studies using high spatial
resolution ground- and space-based observations of local AGN show that Seyfert
class and the "core" (r<~1 kpc) host-galaxy morphology are correlated.
Currently, this relationship has only been established qualitatively, by visual
inspection of the core morphologies of low redshift (z<0.035) Seyfert host
galaxies (Malkan et al. 1998). We re-establish this empirical relationship in
Hubble Space Telescope (HST) optical imaging by visual inspection of a catalog
of 85 local (D<63 Mpc) Seyfert galaxies. We also attempt to re-establish the
core morphology-Seyfert class relationship using an automated, non-parametric
technique that combines both existing classification parameters methods (the
adapted CAS, G-M20), and a new method which implements the Source Extractor
software for feature detection in unsharp-mask images. This new method is
designed explicitly to detect dust features in the images. We use our automated
approach to classify the morphology of the AGN cores and determine that Sy2
galaxies visually appear, on average, to have more dust features than Sy1. With
the exception of this "dustiness" however, we do not measure a strong
correlation between the dust morphology and the Seyfert class of the host
galaxy using quantitative techniques. We discuss the implications of these
results in the context of the Unified Model. |
Search for Low-Mass Dark Matter with CsI(Tl) Crystal Detectors: We present a search for low-mass ($\leq 20 GeV/c^{2}$) weakly interacting
massive particles(WIMPs), strong candidates of dark matter particles,using the
low-background CsI(Tl) detector array of the Korea Invisible Mass Search (KIMS)
experiment. With a total data exposure of 24,324.3kg$\cdot$days,we search for
WIMP interaction signals produced by nuclei recoiling from WIMP-nuclear elastic
scattering with visible energies between 2 and 4keV. The observed energy
distribution of candidate events is consistent with null signals, and upper
limits of the WIMP-proton spin-independent interaction are set with a 90%
confidence level. The observed limit rejects most of the low mass region of
parameter space favored by the DAMA annual modulation signal. | Comment on "Constraining the smoothness parameter and dark energy using
observational H(z) data": In this Comment we discuss a recent analysis by Yu et al. [RAA 11, 125
(2011)] about constraints on the smoothness $\alpha$ parameter and dark energy
models using observational $H(z)$ data. It is argued here that their procedure
is conceptually inconsistent with the basic assumptions underlying the adopted
Dyer-Roeder approach. In order to properly quantify the influence of the $H(z)$
data on the smoothness $\alpha$ parameter, a $\chi^2$-test involving a sample
of SNe Ia and $H(z)$ data in the context of a flat $\Lambda$CDM model is
reanalyzed. This result is confronted with an earlier approach discussed by
Santos et al. (2008) without $H(z)$ data. In the ($\Omega_m, \alpha$) plane, it
is found that such parameters are now restricted on the intervals $0.66 \leq
\alpha \leq 1.0$ and $0.27 \leq \Omega_m \leq 0.37$ within 95.4% confidence
level (2$\sigma$), and, therefore, fully compatible with the homogeneous case.
The basic conclusion is that a joint analysis involving $H(z)$ data can
indirectly improve our knowledge about the influence of the inhomogeneities.
However, this happens only because the $H(z)$ data provide tighter constraints
on the matter density parameter $\Omega_m$. |
Constraining spatial curvature with large-scale structure: We analyse the clustering of matter on large scales in an extension of the
concordance model that allows for spatial curvature. We develop a consistent
approach to curvature and wide-angle effects on the galaxy 2-point correlation
function in redshift space. In particular we derive the Alcock-Paczynski
distortion of $f\sigma_{8}$, which differs significantly from empirical models
in the literature. A key innovation is the use of the `Clustering Ratio', which
probes clustering in a different way to redshift-space distortions, so that
their combination delivers more powerful cosmological constraints. We use this
combination to constrain cosmological parameters, without CMB information. In a
curved Universe, we find that $\Omega_{{\rm m}, 0}=0.26\pm 0.04$ (68\% CL).
When the clustering probes are combined with low-redshift background probes --
BAO and SNIa -- we obtain a CMB-independent constraint on curvature:
$\Omega_{K,0} = 0.0041\,_{-0.0504}^{+0.0500}$. We find no Bayesian evidence
that the flat concordance model can be rejected. In addition we show that the
sound horizon at decoupling is $r_{\rm d} = 144.57 \pm 2.34 \; {\rm Mpc}$, in
agreement with its measurement from CMB anisotropies. As a consequence, the
late-time Universe is compatible with flat $\Lambda$CDM and a standard sound
horizon, leading to a small value of $H_{0}$, {\em without} assuming any CMB
information. Clustering Ratio measurements produce the only low-redshift
clustering data set that is not in disagreement with the CMB, and combining the
two data sets we obtain $\Omega_{K,0}= -0.023 \pm 0.010$. | Anisotropy in the matter distribution beyond the baryonic acoustic
oscillation scale: Tracing the cosmic evolution of the Baryonic Acoustic Oscillation (BAO) scale
with galaxy two point correlation functions is currently the most promising
approach to detect dark energy at early times. A number of ongoing and future
experiments will measure the BAO peak with unprecedented accuracy. We show
based on a set of N-Body simulations that the matter distribution is
anisotropic out to ~150 Mpc/h, far beyond the BAO scale of ~100M pc/h, and
discuss implications for the measurement of the BAO. To that purpose we use
alignment correlation functions, i.e., cross correlation functions between high
density peaks and the overall matter distribution measured along the
orientation of the peaks and perpendicular to it. The correlation function
measured along (perpendicular to) the orientation of high density peaks is
enhanced (reduced) by a factor of ~2 compared to the conventional correlation
function and the location of the BAO peak shifts towards smaller (larger)
scales if measured along (perpendicular to) the orientation of the high density
peaks. Similar effects are expected to shape observed galaxy correlation
functions at BAO scales. |
A closer look at interacting dark energy with statefinder hierarchy and
growth rate of structure: We investigate the interacting dark energy models by using the diagnostics of
statefinder hierarchy and growth rate of structure. We wish to explore the
deviations from $\Lambda$CDM and to differentiate possible degeneracies in the
interacting dark energy models with the geometrical and structure growth
diagnostics. We consider two interacting forms for the models, i.e., $Q_1=\beta
H\rho_c$ and $Q_2=\beta H\rho_{de}$, with $\beta$ being the dimensionless
coupling parameter. Our focus is the I$\Lambda$CDM model that is a
one-parameter extension to $\Lambda$CDM by considering a direct coupling
between the vacuum energy ($\Lambda$) and cold dark matter (CDM), with the only
additional parameter $\beta$. But we begin with a more general case by
considering the I$w$CDM model in which dark energy has a constant $w$
(equation-of-state parameter). For calculating the growth rate of structure, we
employ the "parametrized post-Friedmann" theoretical framework for interacting
dark energy to numerically obtain the $\epsilon(z)$ values for the models. We
show that in both geometrical and structural diagnostics the impact of $w$ is
much stronger than that of $\beta$ in the I$w$CDM model. We thus wish to have a
closer look at the I$\Lambda$CDM model by combining the geometrical and
structural diagnostics. We find that the evolutionary trajectories in the
$S^{(1)}_3$--$\epsilon$ plane exhibit distinctive features and the departures
from $\Lambda$CDM could be well evaluated, theoretically, indicating that the
composite null diagnostic $\{S^{(1)}_3, \epsilon\}$ is a promising tool for
investigating the interacting dark energy models. | Estimating weak lensing convergence correlation of Type-Ia supernovae
from 5-year SNLS data by internal error estimate technique: We report non-zero weak lensing convergence correlation signal of Type-Ia
supernovae from 5-year Supernovae Legacy Survey data. For our analysis we
utilize 296 supernovae magnification data from 5-year SNLS in the weak lensing
limit. The data we use consists of measurements from four different patches,
each covering 1 square degree of the sky, merged together. We demonstrate that
it is possible to have a very good estimate of the two point correlation
function from this data using internal error estimate technique. In order to
have a good estimate of the corresponding covariance matrix we apply bootstrap
spatial re-sampling technique where we reshuffle the original data consisting
of 296 data points 100-10000 times and compare the results with that obtained
from original data points. We show that this technique helps us arrive at a
reliable conclusion on weak lensing convergence even though the original
dataset comprises of a small number of data points. This also allows us to
compute the corresponding covariance matrix with great accuracy. |
The Highest Resolution Mass Map of Galaxy Cluster Substructure To Date
Without Assuming Light Traces Mass: LensPerfect Analysis of Abell 1689: We present a strong lensing mass model of Abell 1689 which resolves
substructures ~25 kpc across (including about ten individual galaxy subhalos)
within the central ~400 kpc diameter. We achieve this resolution by perfectly
reproducing the observed (strongly lensed) input positions of 168 multiple
images of 55 knots residing within 135 images of 42 galaxies. Our model makes
no assumptions about light tracing mass, yet we reproduce the brightest visible
structures with some slight deviations. A1689 remains one of the strongest
known lenses on the sky, with an Einstein radius of RE = 47.0" +/- 1.2" (143
+3/-4 kpc) for a lensed source at zs = 2. We find a single NFW or Sersic prole
yields a good fit simultaneously (with only slight tension) to both our strong
lensing (SL) mass model and published weak lensing (WL) measurements at larger
radius (out to the virial radius). According to this NFW fit, A1689 has a mass
of Mvir = 2.0 +0.5/-0.3 x 10^15 Msun / h70 (M200 = 1.8 +0.4/-0.3 x 10^15 Msun /
h70) within the virial radius rvir = 3.0 +/- 0.2 Mpc / h70 (r200 = 2.4
+0.1/-0.2 Mpc / h70), and a central concentration cvir = 11.5 +1.5/-1.4 (c200 =
9.2 +/- 1.2). Our SL model prefers slightly higher concentrations than previous
SL models, bringing our SL+WL constraints in line with other recent
derivations. Our results support those of previous studies which find A1689 has
either an anomalously large concentration or significant extra mass along the
line of sight (perhaps in part due to triaxiality). If clusters are generally
found to have higher concentrations than realized in simulations, this could
indicate they formed earlier, perhaps as a result of early dark energy. | Groups of dwarf galaxies in the Local supercluster: We present a project on study of groups composed of dwarf galaxies only. We
selected such structures using HyperLEDA and NED databases with visual
inspection on SDSS images and on digital copy of POSS. The groups are
characterized by size of few tens of kpc and line-of-sight velocity dispersion
about 18 km/s. Our groups similar to associations of nearby dwarfs from Tully
et al. (2006). This specific population of multiple dwarf galaxies such as
IZw18 may contain significant amount of dark matter. It is very likely that we
see them at the stage just before merging of its components. |
Nonlinear effects of dark energy clustering beyond the acoustic scales: We extend the resummation method of Anselmi & Pietroni (2012) to compute the
total density power spectrum in models of quintessence characterized by a
vanishing speed of sound. For standard $\Lambda$CDM cosmologies, this
resummation scheme allows predictions with an accuracy at the few percent level
beyond the range of scales where acoustic oscillations are present, therefore
comparable to other, common numerical tools. In addition, our theoretical
approach indicates an approximate but valuable and simple relation between the
power spectra for standard quintessence models and models where scalar field
perturbations appear at all scales. This, in turn, provides an educated guess
for the prediction of nonlinear growth in models with generic speed of sound,
particularly valuable since no numerical results are yet available. | A Measurement of the Galaxy Group-Thermal Sunyaev-Zel'dovich Effect
Cross-Correlation Function: Stacking cosmic microwave background (CMB) maps around known galaxy clusters
and groups provides a powerful probe of the distribution of hot gas in these
systems via the Sunyaev-Zel'dovich (SZ) effect. A stacking analysis allows one
to detect the average SZ signal around low mass halos, and to extend
measurements out to large scales, which are too faint to detect individually in
the SZ or in X-ray emission. In addition, cross correlations between SZ maps
and other tracers of large-scale structure (with known redshifts) can be used
to extract the redshift-dependence of the SZ background. Motivated by these
exciting prospects, we measure the two-point cross-correlation function between
a catalog of $\sim 380,000$ galaxy groups (with redshifts spanning
$z=0.01-0.2$) from the Sloan Digital Sky Survey (SDSS) and Compton-y parameter
maps constructed by the Planck collaboration. We find statistically significant
correlations between the group catalog and Compton-y maps in each of six
separate mass bins, with estimated halo masses in the range $10^{11.5-15.5}
M_\odot/h$. We compare these measurements with halo models of the SZ signal,
which describe the stacked measurement in terms of one-halo and two-halo terms.
The one-halo term quantifies the average pressure profile around the groups in
a mass bin, while the two-halo term describes the contribution of correlated
neighboring halos. For the more massive groups we find clear evidence for the
one- and two-halo regimes, while groups with mass below $10^{13} M_\odot/h$ are
dominated by the two-halo term given the resolution of Planck data. We use the
signal in the two-halo regime to determine the bias-weighted electron pressure
of the universe: $\langle b P_e \rangle= 1.50 \pm 0.226 \times 10^{-7}$ keV
cm$^{-3}$ (1-$\sigma$) at $z\approx 0.15$. |
Mirror dark matter explanation of the DAMA, CoGeNT and CRESST-II data: Dark matter might reside in a hidden sector which contains an unbroken
$U(1)'$ gauge interaction kinetically mixed with standard $U(1)_Y$. Mirror dark
matter provides a well motivated example of such a theory. We show that the
DAMA, CoGeNT and CRESST-II experiments can be simultaneously explained within
this hidden sector framework. An experiment in the Southern Hemisphere is
needed to test this explanation via a diurnal modulation signal. | HI intensity mapping with MeerKAT: Calibration pipeline for multi-dish
autocorrelation observations: While most purpose-built 21cm intensity mapping experiments are close-packed
interferometer arrays, general-purpose dish arrays should also be capable of
measuring the cosmological 21cm signal. This can be achieved most efficiently
if the array is used as a collection of scanning autocorrelation dishes rather
than as an interferometer. As a first step towards demonstrating the
feasibility of this observing strategy, we show that we are able to
successfully calibrate dual-polarisation autocorrelation data from 64 MeerKAT
dishes in the L-band (856-1712 MHz, 4096 channels), with 10.5 hours of data
retained from six nights of observing. We describe our calibration pipeline,
which is based on multi-level RFI flagging, periodic noise diode injection to
stabilise gain drifts and an absolute calibration based on a multi-component
sky model. We show that it is sufficiently accurate to recover maps of diffuse
celestial emission and point sources over a 10 deg x 30 deg patch of the sky
overlapping with the WiggleZ 11hr field. The reconstructed maps have a good
level of consistency between per-dish maps and external datasets, with the
estimated thermal noise limited to 1.4 x the theoretical noise level (~ 2 mK).
The residual maps have rms amplitudes below 0.1 K, corresponding to <1% of the
model temperature. The reconstructed Galactic HI intensity map shows excellent
agreement with the Effelsberg-Bonn HI Survey, and the flux of the radio galaxy
4C+03.18 is recovered to within 3.6%, which demonstrates that the
autocorrelation can be successfully calibrated to give the zero-spacing flux
and potentially help in the imaging of MeerKAT interferometric data. Our
results provide a positive indication towards the feasibility of using MeerKAT
and the future SKA to measure the HI intensity mapping signal and probe
cosmology on degree scales and above. |
Optical multiband surface photometry of a sample of Seyfert galaxies. I.
Large-scale morphology and local environment analysis of matched Seyfert and
inactive galaxy samples: Parallel analysis of the large-scale morphology and local environment of
matched active and control galaxy samples plays an important role in studies of
the fueling of active galactic nuclei. We carry out a detailed morphological
characterization of a sample of 35 Seyfert galaxies and a matched sample of
inactive galaxies in order to compare the evidence of non-axisymmetric
perturbation of the potential and, in the second part of this paper, to be able
to perform a multicomponent photometric decomposition of the Seyfert galaxies.
We constructed contour maps, BVRcIc profiles of the surface brightness,
ellipticity, and position angle, as well as colour index profiles. We further
used colour index images, residual images, and structure maps, which helped
clarify the morphology of the galaxies. We studied the presence of close
companions using literature data. By straightening out the morphological status
of some of the objects, we derived an improved morphological classification and
built a solid basis for a further multicomponent decomposition of the Seyfert
sample. We report hitherto undetected (to our knowledge) structural components
in some Seyfert galaxies - a bar (Ark 479), an oval/lens (Mrk 595), rings (Ark
120, Mrk 376), a nuclear bar and ring (Mrk 352), and nuclear dust lanes (Mrk
590). We compared the large-scale morphology and local environment of the
Seyfert sample to those of the control one and found that (1) the two samples
show similar incidences of bars, rings, asymmetries, and close companions; (2)
the Seyfert bars are generally weaker than the bars of the control galaxies;
(3) the bulk of the two samples shows morphological evidence of
non-axisymmetric perturbations of the potential or close companions; (4) the
fueling of Seyfert nuclei is not directly related to the large-scale morphology
and local environment of their host galaxies. | On the Analysis of DLA Kinematics: We discuss two mistreatments of damped Lya (DLA) kinematic analysis that were
first performed by Haehnelt, Steinmetz, & Rauch (1998; hereafter HSR98) and
have recently been repeated by Hong et al. (2010; arXiv:1008.4242v1,
arXiv:1008.4242v2; hereafter H10). Each mistreatment led to the improper
excising of simulated absorption profiles. Specifically, their analyses are
strictly biased against DLA sightlines that have low HI column density log NHI
< 20.5, very high NHI values, and (for all NHI) sightlines with low velocity
width Dv (<30 km/s for HSR98; <[20-30] km/s for H10). None of these biases
exist in the observational analysis. We suspect these mistreatments compromise
the results that followed. Hopefully this posting will prevent their repetition
in the future. |
Non-Gaussianity from extragalactic point-sources: The population of compact extragalactic sources contribute to the
non-Gaussianity at Cosmic Microwave Background frequencies. We study their
non-Gaussianity using publicly available full-sky simulations. We introduce a
parametrisation to visualise efficiently the bispectrum and we describe the
scale and frequency dependences of the bispectrum of radio and IR
point-sources. We show that the bispectrum is well fitted by an analytical
prescription. We find that the clustering of IR sources enhances their
non-Gaussianity by several orders of magnitude, and that their bispectrum peaks
in the squeezed triangles. Examining the impact of these sources on primordial
non-Gaussianity estimation, we find that radio sources yield an important
positive bias to local fNL at low frequencies but this bias is efficiently
reduced by masking detectable sources. IR sources produce a negative bias at
high frequencies, which is not dimmed by the masking, as their clustering is
dominated by faint sources. | The Equation of State of Tracker Fields: We derive the equation of state of tracker fields, which are typical examples
of freezing quintessence (quintessence with the equation of state approaching
toward -1), taking into account of the late-time departure from the tracker
solution due to the nonzero density parameter of dark energy $\Omp$. We
calculate the equation of state as a function of $\Omp$ for constant
$\Gamma=VV"/(V')^2$ (during matter era) models. The derived equation of state
contains a single parameter, $w_{(0)}$, which parametrizes the equation of
state during the matter-dominated epoch. We derive observational constraints on
$w_{(0)}$ and find that observational data are consistent with the cosmological
constant: $-1.11< \wzero< -0.96 (1 \sigma)$. |
Photometric classification and redshift estimation of LSST Supernovae: Supernova (SN) classification and redshift estimation using photometric data
only have become very important for the Large Synoptic Survey Telescope (LSST),
given the large number of SNe that LSST will observe and the impossibility of
spectroscopically following up all the SNe. We investigate the performance of a
SN classifier that uses SN colors to classify LSST SNe with the Random Forest
classification algorithm. Our classifier results in an AUC of 0.98 which
represents excellent classification. We are able to obtain a photometric SN
sample containing 99$\%$ SNe Ia by choosing a probability threshold. We
estimate the photometric redshifts (photo-z) of SNe in our sample by fitting
the SN light curves using the SALT2 model with nested sampling. We obtain a
mean bias ($\left<z_\mathrm{phot}-z_\mathrm{spec}\right>$) of 0.012 with
$\sigma\left( \frac{z_\mathrm{phot}-z_\mathrm{spec}}{1+z_\mathrm{spec}}\right)
= 0.0294$ without using a host-galaxy photo-z prior, and a mean bias
($\left<z_\mathrm{phot}-z_\mathrm{spec}\right>$) of 0.0017 with $\sigma\left(
\frac{z_\mathrm{phot}-z_\mathrm{spec}}{1+z_\mathrm{spec}}\right) = 0.0116$
using a host-galaxy photo-z prior. Assuming a flat $\Lambda CDM$ model with
$\Omega_m=0.3$, we obtain $\Omega_m$ of $0.305\pm0.008$ (statistical errors
only), using the simulated LSST sample of photometric SNe Ia (with intrinsic
scatter $\sigma_\mathrm{int}=0.11$) derived using our methodology without using
host-galaxy photo-z prior. Our method will help boost the power of SNe from the
LSST as cosmological probes. | Galaxy formation on the largest scales: The impact of astrophysics on
the BAO peak: We investigate the effects of galaxy formation on the baryonic acoustic
oscillations (BAO) peak by applying semi-analytic modelling techniques to the
Millennium-XXL, a $3 \times 10^{11}$ particle N-body simulation of similar
volume to the future EUCLID survey. Our approach explicitly incorporates the
effects of tidal fields and stochasticity on halo formation, as well as the
presence of velocity bias, spatially correlated merger histories, and the
connection of all these with the observable and physical properties of
galaxies. We measure significant deviations in the shape of the BAO peak from
the expectations of a linear bias model built on top of the nonlinear dark
matter distribution. We find that the galaxy correlation function shows an
excess close to the maximum of the BAO peak ($r\sim110 Mpc/h$) and a deficit at
$r\sim90 Mpc/h$. Depending on the redshift, selection criteria and number
density of the galaxy samples, these bias distortions can be up to 5% in
amplitude. They are, however, largely absorbed by marginalization over nuisance
parameters in current analytical modelling of the BAO peak in configuration
space, in particular into the parameter that controls the broadening due to
nonlinear evolution. As a result, the galaxy formation effects detected here
are unlikely to bias the high-precision measurements planned by the upcoming
generation of wide-field galaxy surveys. |
Cumulative effects in inflation with ultra-light entropy modes: In multi-field inflation one or more non-adiabatic modes may become light,
potentially inducing large levels of isocurvature perturbations in the cosmic
microwave background. If in addition these light modes are coupled to the
adiabatic mode, they influence its evolution on super horizon scales. Here we
consider the case in which a non-adiabatic mode becomes approximately massless
("ultralight") while still coupled to the adiabatic mode, a typical situation
that arises with pseudo-Nambu-Goldstone bosons or moduli. This ultralight mode
freezes on super-horizon scales and acts as a constant source for the curvature
perturbation, making it grow linearly in time and effectively suppressing the
isocurvature component. We identify a Stuckelberg-like emergent shift symmetry
that underlies this behavior. As inflation lasts for many e-folds, the
integrated effect of this source enhances the power spectrum of the adiabatic
mode, while keeping the non-adiabatic spectrum approximately untouched. In this
case, towards the end of inflation all the fluctuations, adiabatic and
non-adiabatic, are dominated by a single degree of freedom. | How rare is the Bullet Cluster (in a $Λ$CDM universe)?: The Bullet Cluster (1E0657-56) is well-known as providing visual evidence of
dark matter but it is potentially incompatible with the standard $\Lambda$CDM
cosmology due to the high relative velocity of the two colliding clusters.
Previous studies have focussed on the probability of such a high relative
velocity amongst selected candidate systems. This notion of `probability' is
however difficult to interpret and can lead to paradoxical results. Instead, we
consider the expected number of Bullet-like systems on the sky up to a
specified redshift, which allows for direct comparison with observations. Using
a Hubble volume N-body simulation with high resolution we investigate how the
number of such systems depends on the masses of the halo pairs, their
separation, and collisional angle. This enables us to extract an approximate
formula for the expected number of halo-halo collisions given specific
collisional parameters. We use extreme value statistics to analyse the tail of
the pairwise velocity distribution and demonstrate that it is fatter than the
previously assumed Gaussian form. We estimate that the number of dark matter
halo pairs as or more extreme than 1E0657-56 in mass, separation and relative
velocity is $1.3^{+2.0}_{-0.6}$ up to redshift $z=0.3$. However requiring the
halos to have collided and passed through each other as is observed decreases
this number to only 0.1. The discovery of more such systems would thus indeed
present a challenge to the standard cosmology. |
The large-separation expansion of peak clustering in Gaussian random
fields: In the peaks approach, the formation sites of observable structures in the
Universe are identified as peaks in the matter density field. The statistical
properties of the clustering of peaks are particularly important in this
respect. In this paper, we investigate the large-separation expansion of the
correlation function of peaks in Gaussian random fields. The analytic formula
up to third order is derived, and the resultant expression can be evaluated by
a combination of one-dimensional fast Fourier transforms, which are evaluated
very fast. The analytic formula obtained perturbatively in the large-separation
limit is compared with a method of Monte-Carlo integrations, and a
complementarity between the two methods is demonstrated. | Higgs Inflation, Quantum Smearing and the Tensor to Scalar Ratio: In cosmic inflation driven by a scalar gauge singlet field with a tree level
Higgs potential, the scalar to tensor ratio r is estimated to be larger than
0.036, provided the scalar spectral index n_s >= 0.96. We discuss quantum
smearing of these predictions arising from the inflaton couplings to other
particles such as GUT scalars, and show that these corrections can
significantly decrease r. However, for n_s >= 0.96, we obtain r >= 0.02 which
can be tested by the Planck satellite. |
A study of cool core resiliency and entropy mixing in simulations of
galaxy cluster mergers: We present results from a suite of binary merging cluster simulations. The
hydrodynamical cluster simulations are performed employing a smoothed particle
hydrodynamics (SPH) formulation in which gradient errors are strongly reduced
by means of an integral approach. We consider adiabatic as well as radiative
simulations, in which we include gas cooling, star formation and energy
feedback from supernovae. We explore the effects of merging on the
thermodynamic structure of the intracluster gas of the final merger remnant. In
particular, we study how core entropy is generated during the merging and the
stability properties of the initial cool-core profile against disruption. To
this end, we consider a range of initial mass ratio and impact parameters.
Final entropy profiles of our adiabatic merging simulations are in good accord
with previous findings (ZuHone 2011), with cool-cores being disrupted for all
of the initial merging setups. For equal-mass off-axis mergers, we find that a
significant contribution to the final primary core entropy is due to
hydrodynamic instabilities generated by rotational motions, which are induced
by tidal torques during the first pericenter passage. In radiative simulations,
cool-cores are more resilient against heating processes; nonetheless, they are
able to maintain their integrity only in the case of off-axis mergers with very
unequal masses. We suggest that these results are robust against changes in the
gas physical modeling, in particular to the inclusion of AGN thermal feedback.
Our findings support the view that the observed core cluster morphology
emerges naturally in a merging cluster context, and conclude that the merging
angular momentum is a key parameter in shaping the thermodynamical properties
of the final merger remnant. | Cosmological parameters from weak cosmological lensing: In this manuscript of the habilitation \`a diriger des recherches (HDR), the
author presents some of his work over the last ten years. The main topic of
this thesis is cosmic shear, the distortion of images of distant galaxies due
to weak gravitational lensing by the large-scale structure in the Universe.
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.
I review the principles of weak gravitational lensing and show how cosmic
shear is interpreted in a cosmological context. Then I give an overview of
weak-lensing measurements, and present observational results from the
Canada-France Hawai'i Lensing Survey (CFHTLenS), as well as the implications
for cosmology. I 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. |
Inner Polar Rings and Disks: Observed Properties: A list of galaxies with inner regions revealing polar (or strongly inclined
to the main galactic plane) disks and rings is compiled from the literature
data. The list contains 47 galaxies of all morphological types, from E to Irr.
We consider the statistics of the parameters of polar structures known from
observations. The radii of the majority of them do not exceed 1.5 kpc. The
polar structures are equally common in barred and unbarred galaxies. At the
same time, if a galaxy has a bar (or a triaxial bulge), this leads to the polar
disk stabilization - its axis of rotation usually coincides with the major axis
of the bar. More than two thirds of all considered galaxies reveal one or
another sign of recent interaction or merging. This fact indicates a direct
relation between the external environment and the presence of an inner polar
structure. | Ruling out the power-law form of the scalar primordial spectrum: Combining Planck CMB temperature [1] and BICEP2 B-mode polarization data
[2,3] we show qualitatively that, assuming inflationary consistency relation,
the power-law form of the scalar primordial spectrum is ruled out at more than
$3\sigma$ CL. This is an important finding, since the power-law form of the
scalar primordial spectrum is one of the main assumptions of concordance model
of cosmology and also a direct prediction of many inflationary scenarios. We
show that a break or step in the form of the primordial scalar perturbation
spectrum, similar to what we studied recently analyzing Planck data [4] can
address both Planck and BICEP2 results simultaneously. Our findings also
indicate that the data may require more flexibilities than what running of
scalar spectral index can provide. Finally we show that an inflaton potential,
originally appeared in [5] can generate both the step and the break model of
scalar primordial spectrum in two different limits. The discussed potential is
found to be favored by Planck data but marginally disfavored by BICEP2 results
as it produces slightly lower amplitude of tensor primordial spectrum. Hence,
if the tensor-to-scalar ratio ($r$) quoted by BICEP2 persists, it is of
importance that we generate inflationary models with large $r$ and at the same
time provide suppression in scalar primordial spectrum at large scales. |
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