73 research outputs found
Sparse Bayesian mass-mapping with uncertainties: hypothesis testing of structure
A crucial aspect of mass-mapping, via weak lensing, is quantification of the
uncertainty introduced during the reconstruction process. Properly accounting
for these errors has been largely ignored to date. We present results from a
new method that reconstructs maximum a posteriori (MAP) convergence maps by
formulating an unconstrained Bayesian inference problem with Laplace-type
-norm sparsity-promoting priors, which we solve via convex
optimization. Approaching mass-mapping in this manner allows us to exploit
recent developments in probability concentration theory to infer theoretically
conservative uncertainties for our MAP reconstructions, without relying on
assumptions of Gaussianity. For the first time these methods allow us to
perform hypothesis testing of structure, from which it is possible to
distinguish between physical objects and artifacts of the reconstruction. Here
we present this new formalism, demonstrate the method on illustrative examples,
before applying the developed formalism to two observational datasets of the
Abel-520 cluster. In our Bayesian framework it is found that neither Abel-520
dataset can conclusively determine the physicality of individual local massive
substructure at significant confidence. However, in both cases the recovered
MAP estimators are consistent with both sets of data
CFHTLenS: Co-evolution of galaxies and their dark matter haloes
Galaxy-galaxy weak lensing is a direct probe of the mean matter distribution
around galaxies. The depth and sky coverage of the CFHT Legacy Survey yield
statistically significant galaxy halo mass measurements over a much wider range
of stellar masses ( to ) and redshifts () than previous weak lensing studies. At redshift , the
stellar-to-halo mass ratio (SHMR) reaches a maximum of percent as a
function of halo mass at . We find, for the first
time from weak lensing alone, evidence for significant evolution in the SHMR:
the peak ratio falls as a function of cosmic time from percent at
to percent at , and shifts to lower
stellar mass haloes. These evolutionary trends are dominated by red galaxies,
and are consistent with a model in which the stellar mass above which star
formation is quenched "downsizes" with cosmic time. In contrast, the SHMR of
blue, star-forming galaxies is well-fit by a power law that does not evolve
with time. This suggests that blue galaxies form stars at a rate that is
balanced with their dark matter accretion in such a way that they evolve along
the SHMR locus. The redshift dependence of the SHMR can be used to constrain
the evolution of the galaxy population over cosmic time.Comment: 18 pages, MNRAS, in pres
Perturbation theory for cosmologies with nonlinear structure
The next generation of cosmological surveys will operate over unprecedented
scales, and will therefore provide exciting new opportunities for testing
general relativity. The standard method for modelling the structures that these
surveys will observe is to use cosmological perturbation theory for linear
structures on horizon-sized scales, and Newtonian gravity for non-linear
structures on much smaller scales. We propose a two-parameter formalism that
generalizes this approach, thereby allowing interactions between large and
small scales to be studied in a self-consistent and well-defined way. This uses
both post-Newtonian gravity and cosmological perturbation theory, and can be
used to model realistic cosmological scenarios including matter, radiation and
a cosmological constant. We find that the resulting field equations can be
written as a hierarchical set of perturbation equations. At leading-order,
these equations allow us to recover a standard set of Friedmann equations, as
well as a Newton-Poisson equation for the inhomogeneous part of the Newtonian
energy density in an expanding background. For the perturbations in the
large-scale cosmology, however, we find that the field equations are sourced by
both non-linear and mode-mixing terms, due to the existence of small-scale
structures. These extra terms should be expected to give rise to new
gravitational effects, through the mixing of gravitational modes on small and
large scales - effects that are beyond the scope of standard linear
cosmological perturbation theory. We expect our formalism to be useful for
accurately modelling gravitational physics in universes that contain non-linear
structures, and for investigating the effects of non-linear gravity in the era
of ultra-large-scale surveys.Comment: "21 pages, 2 appendices. Equations (29) and (80) have been corrected
from the published version.
Heritage Quay: What Will You Discover? Transforming the Archives of the University of Huddersfield, Yorkshire, UK
The Heritage Quay project is changing how archive services at the University of Huddersfield are delivered. This article examines how the Staff/Space/Collections dependency model and Customer Service Excellence framework have been used, and what lessons can be drawn for other archives
CFHTLenS: co-evolution of galaxies and their dark matter haloes
Galaxy-galaxy weak lensing is a direct probe of the mean matter distribution around galaxies. The depth and sky coverage of the Canada-France-Hawaii Telescope Legacy Survey yield statistically significant galaxy halo mass measurements over a much wider range of stellar masses (108.75 to 1011.3âMâ) and redshifts (0.2<z<0.8) than previous weak lensing studies. At redshift zâŒ0.5, the stellar-to-halo mass ratio (SHMR) reaches a maximum of 4.0±0.2âperâcent as a function of halo mass at âŒ1012.25âMâ. We find, for the first time from weak lensing alone, evidence for significant evolution in the SHMR: the peak ratio falls as a function of cosmic time from 4.5±0.3âperâcent at zâŒ0.7 to 3.4±0.2âperâcent at zâŒ0.3, and shifts to lower stellar mass haloes. These evolutionary trends are dominated by red galaxies, and are consistent with a model in which the stellar mass above which star formation is quenched âdownsizes' with cosmic time. In contrast, the SHMR of blue, star-forming galaxies is well fitted by a power law that does not evolve with time. This suggests that blue galaxies form stars at a rate that is balanced with their dark matter accretion in such a way that they evolve along the SHMR locus. The redshift dependence of the SHMR can be used to constrain the evolution of the galaxy population over cosmic tim
Radiative Kaon Decays and the Penguin Contribution to the Delta I = 1/2 Rule
A consistent census of penguins in the Delta I = 1/2 rule is taken from the
eta0 pole contribution to the radiative KL to gamma gamma, KS to pi0 gamma
gamma and K+ to pi+ gamma gamma decay modes. We briefly comment on its impact
for KL to pi0 pi0 gamma gamma, KL to pi+ pi- gamma and check its compatibility
with the KL - KS mass difference and the CP violating epsilon-prime / epsilon
parameter.Comment: 37 pages, 16 figure
CFHTLenS: the environmental dependence of galaxy halo masses from weak lensing
We use weak gravitational lensing to analyse the dark matter haloes around satellite galaxies in galaxy groups in the CanadaâFranceâHawaii Telescope Lensing Survey (CFHTLenS) data set. This data set is derived from the CanadaâFranceâHawaii Telescope Legacy Survey Wide survey, and encompasses 154 deg^2 of high-quality shape data. Using the photometric redshifts, we divide the sample of lens galaxies with stellar masses in the range 10^(9)â10^(10.5)âM_â into those likely to lie in high-density environments (HDE) and those likely to lie in low-density environments (LDE). Through comparison with galaxy catalogues extracted from the Millennium Simulation, we show that the sample of HDE galaxies should primarily (âŒ61âperâcent) consist of satellite galaxies in groups, while the sample of LDE galaxies should consist of mostly (âŒ87âperâcent) non-satellite (field and central) galaxies. Comparing the lensing signals around samples of HDE and LDE galaxies matched in stellar mass, the lensing signal around HDE galaxies clearly shows a positive contribution from their host groups on their lensing signals at radii of âŒ500â1000 kpc, the typical separation between satellites and group centres. More importantly, the subhaloes of HDE galaxies are less massive than those around LDE galaxies by a factor of 0.65 ± 0.12, significant at the 2.9Ï level. A natural explanation is that the haloes of satellite galaxies are stripped through tidal effects in the group environment. Our results are consistent with a typical tidal truncation radius of âŒ40 kpc
CFHTLenS: combined probe cosmological model comparison using 2D weak gravitational lensing
We present cosmological constraints from 2D weak gravitational lensing by the large-scale structure in the CanadaâFranceâHawaii Telescope Lensing Survey (CFHTLenS) which spans 154 deg^2 in five optical bands. Using accurate photometric redshifts and measured shapes for 4.2 million galaxies between redshifts of 0.2 and 1.3, we compute the 2D cosmic shear correlation function over angular scales ranging between 0.8 and 350 arcmin. Using non-linear models of the dark-matter power spectrum, we constrain cosmological parameters by exploring the parameter space with Population Monte Carlo sampling. The best constraints from lensing alone are obtained for the small-scale density-fluctuations amplitude Ï_8 scaled with the total matter density Ωm. For a flat Îcold dark matter (ÎCDM) model we obtain Ï_8(Ω_m/0.27)0.6 = 0.79 ± 0.03.
We combine the CFHTLenS data with 7-year Wilkinson Microwave Anisotropy Probe (WMAP7), baryonic acoustic oscillations (BAO): SDSS-III (BOSS) and a Hubble Space Telescope distance-ladder prior on the Hubble constant to get joint constraints. For a flat ÎCDM model, we find Ω_m = 0.283 ± 0.010 and Ï_8 = 0.813 ± 0.014. In the case of a curved wCDM universe, we obtain Ω_m = 0.27 ± 0.03, Ï_8 = 0.83 ± 0.04, w0 = â1.10 ± 0.15 and Ω_K = 0.006^(+0.006)_(â 0.004).
We calculate the Bayesian evidence to compare flat and curved ÎCDM and dark-energy CDM models. From the combination of all four probes, we find models with curvature to be at moderately disfavoured with respect to the flat case. A simple dark-energy model is indistinguishable from ÎCDM. Our results therefore do not necessitate any deviations from the standard cosmological model
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