187 research outputs found
Cosmology in doubly coupled massive gravity: constraints from SNIa, BAO and CMB
Massive gravity in the presence of doubly coupled matter field via en
effective composite metric yields an accelerated expansion of the universe. It
has been recently shown that the model admits stable de Sitter attractor
solutions and could be used as a dark energy model. In this work, we perform a
first analysis of the constraints imposed by the SNIa, BAO and CMB data on the
massive gravity model with the effective composite metric and show that all the
background observations are mutually compatible at the one sigma level with the
model.Comment: 7 pages, 4 figure
Constraining a halo model for cosmological neutral hydrogen
We describe a combined halo model to constrain the distribution of neutral
hydrogen (HI) in the post-reionization universe. We combine constraints from
the various probes of HI at different redshifts: the low-redshift 21-cm
emission line surveys, intensity mapping experiments at intermediate redshifts,
and the Damped Lyman-Alpha (DLA) observations at higher redshifts. We use a
Markov Chain Monte Carlo (MCMC) approach to combine the observations and place
constraints on the free parameters in the model. Our best-fit model involves a
relation between neutral hydrogen mass and halo mass with a
non-unit slope, and an upper and a lower cutoff. We find that the model fits
all the observables but leads to an underprediction of the bias parameter of
DLAs at . We also find indications of a possible tension between
the HI column density distribution and the mass function of HI-selected
galaxies at . We provide the central values of the parameters of the
best-fit model so derived. We also provide a fitting form for the derived
evolution of the concentration parameter of HI in dark matter haloes, and
discuss the implications for the redshift evolution of the HI-halo mass
relation.Comment: 10 pages, 9 figures, 2 tables; version accepted for publication in
MNRA
Integrated cosmological probes: Concordance quantified
Assessing the consistency of parameter constraints derived from different
cosmological probes is an important way to test the validity of the underlying
cosmological model. In an earlier work [Nicola et al., 2017], we computed
constraints on cosmological parameters for CDM from an integrated
analysis of CMB temperature anisotropies and CMB lensing from Planck, galaxy
clustering and weak lensing from SDSS, weak lensing from DES SV as well as Type
Ia supernovae and Hubble parameter measurements. In this work, we extend this
analysis and quantify the concordance between the derived constraints and those
derived by the Planck Collaboration as well as WMAP9, SPT and ACT. As a measure
for consistency, we use the Surprise statistic [Seehars et al., 2014], which is
based on the relative entropy. In the framework of a flat CDM
cosmological model, we find all data sets to be consistent with one another at
a level of less than 1. We highlight that the relative entropy is
sensitive to inconsistencies in the models that are used in different parts of
the analysis. In particular, inconsistent assumptions for the neutrino mass
break its invariance on the parameter choice. When consistent model assumptions
are used, the data sets considered in this work all agree with each other and
CDM, without evidence for tensions.Comment: 17 pages, 4 figures, 2 tables, updated following referee's comments,
now includes discussion of the Riess et al., 2016 Hubble parameter
measurement, matches version accepted by JCA
Cross-correlating 21 cm and galaxy surveys: implications for cosmology and astrophysics
We forecast astrophysical and cosmological parameter constraints from
synergies between 21 cm intensity mapping and wide field optical galaxy surveys
(both spectroscopic and photometric) over . We focus on the
following survey combinations in this work: (i) a CHIME-like and DESI-like
survey in the northern hemisphere, (ii) an LSST-like and SKA I MID-like survey
and (ii) a MeerKAT-like and DES-like survey in the southern hemisphere. We work
with the CDM cosmological model having parameters , parameters and representing the cutoff
and slope of the HI-halo mass relation in the previously developed HI halo
model framework, and a parameter that represents the scale dependence of
the optical galaxy bias. Using a Fisher forecasting framework, we explore (i)
the effects of the HI and galaxy astrophysical uncertainties on the
cosmological parameter constraints, assuming priors from the present knowledge
of the astrophysics, (ii) the improvements on astrophysical constraints over
their current priors in the three configurations considered, (ii) the
tightening of the constraints on the parameters relative to the corresponding
HI auto-correlation surveys alone.Comment: 9 pages, 5 figures, 2 tables; accepted for publication in MNRA
Integrated approach to cosmology: Combining CMB, large-scale structure and weak lensing
Recent observational progress has led to the establishment of the standard
CDM model for cosmology. This development is based on different
cosmological probes that are usually combined through their likelihoods at the
latest stage in the analysis. We implement here an integrated scheme for
cosmological probes, which are combined in a common framework starting at the
map level. This treatment is necessary as the probes are generally derived from
overlapping maps and are thus not independent. It also allows for a thorough
test of the cosmological model and of systematics through the consistency of
different physical tracers. As a first application, we combine current
measurements of the Cosmic Microwave Background (CMB) from the Planck
satellite, and galaxy clustering and weak lensing from SDSS. We consider the
spherical harmonic power spectra of these probes including all six auto- and
cross-correlations along with the associated full Gaussian covariance matrix.
This provides an integrated treatment of different analyses usually performed
separately including CMB anisotropies, cosmic shear, galaxy clustering,
galaxy-galaxy lensing and the Integrated Sachs-Wolfe (ISW) effect with galaxy
and shear tracers. We derive constraints on CDM parameters that are
compatible with existing constraints and highlight tensions between data sets,
which become apparent in this integrated treatment. We discuss how this
approach provides a complete and powerful integrated framework for probe
combination and how it can be extended to include other tracers in the context
of current and future wide field cosmological surveys.Comment: 29 pages, 19 figures, 3 tables, to appear in PRD, updated following
referee's comments including small changes in result
Shapelets: I. A Method for Image Analysis
We present a new method for the analysis of images, a fundamental task in
observational astronomy. It is based on the linear decomposition of each object
in the image into a series of localised basis functions of different shapes,
which we call `Shapelets'. A particularly useful set of complete and
orthonormal shapelets is that consisting of weighted Hermite polynomials, which
correspond to perturbations around a circular gaussian. They are also the
eigenstates of the 2-dimensional Quantum Harmonic Oscillator, and thus allow us
to use the powerful formalism developed for this problem. Among their
remarkable properties, they are invariant under Fourier transforms (up to a
rescaling), leading to an analytic form for convolutions. The generator of
linear transformations such as translations, rotations, shears and dilatations
can be written as simple combinations of raising and lowering operators. We
derive analytic expressions for practical quantities, such as the centroid
(astrometry), flux (photometry) and radius of the object, in terms of its
shapelet coefficients. We also construct polar basis functions which are
eigenstates of the angular momentum operator, and thus have simple properties
under rotations. As an example, we apply the method to Hubble Space Telescope
images, and show that the small number of shapelet coefficients required to
represent galaxy images lead to compression factors of about 40 to 90. We
discuss applications of shapelets for the archival of large photometric
surveys, for weak and strong gravitational lensing and for image deprojection.Comment: 13 Latex pages, including 10 figures and 2 tables. Submitted to
MNRAS. Also available at http://www.ast.cam.ac.uk/~ar
Cosmic Shear with Einstein Rings
We explore a new technique to measure cosmic shear using Einstein rings. In
Birrer et al. (2017), we showed that the detailed modelling of Einstein rings
can be used to measure external shear to high precision. In this letter, we
explore how a collection of Einstein rings can be used as a statistical probe
of cosmic shear. We present a forecast of the cosmic shear information
available in Einstein rings for different strong lensing survey configurations.
We find that, assuming that the number density of Einstein rings in the COSMOS
survey is representative, future strong lensing surveys should have a
cosmological precision comparable to the current ground based weak lensing
surveys. We discuss how this technique is complementary to the standard cosmic
shear analyses since it is sensitive to different systematic and can be used
for cross-calibration.Comment: 4 pages, 1 figure, 1 table. ApJL accepte
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