373 research outputs found
Cosmic Discordance: Are Planck CMB and CFHTLenS weak lensing measurements out of tune?
We examine the level of agreement between low redshift weak lensing data and
the CMB using measurements from the CFHTLenS and Planck+WMAP polarization. We
perform an independent analysis of the CFHTLenS six bin tomography results of
Heymans et al. (2013). We extend their systematics treatment and find the
cosmological constraints to be relatively robust to the choice of non-linear
modeling, extension to the intrinsic alignment model and inclusion of baryons.
We find that the 90% confidence contours of CFHTLenS and Planck+WP do not
overlap even in the full 6-dimensional parameter space of CDM, so the
two datasets are discrepant. Allowing a massive active neutrino or tensor modes
does not significantly resolve the disagreement in the full n-dimensional
parameter space. Our results differ from some in the literature because we use
the full tomographic information in the weak lensing data and marginalize over
systematics. We note that adding a sterile neutrino to CDM does bring
the 8-dimensional 64% contours to overlap, mainly due to the extra effective
number of neutrino species, which we find to be 0.84 0.35 (68%) greater
than standard on combining the datasets. We discuss why this is not a
completely satisfactory resolution, leaving open the possibility of other new
physics or observational systematics as contributing factors. We provide
updated cosmology fitting functions for the CFHTLenS constraints and discuss
the differences from ones used in the literature.Comment: 12 pages, 8 figures. We compare our findings with studies that
include other low redshift probes of structure. An interactive figure is
available at http://bit.ly/1oZH0KQ. This version is that accepted by MNRAS,
and so includes changes based on the referee's comments, and updates to the
analysis cod
S\'{e}rsic galaxy models in weak lensing shape measurement: model bias, noise bias and their interaction
Cosmic shear is a powerful probe of cosmological parameters, but its
potential can be fully utilised only if galaxy shapes are measured with great
accuracy. Two major effects have been identified which are likely to account
for most of the bias for maximum likelihood methods in recent shear measurement
challenges. Model bias occurs when the true galaxy shape is not well
represented by the fitted model. Noise bias occurs due to the non-linear
relationship between image pixels and galaxy shape. In this paper we
investigate the potential interplay between these two effects when an imperfect
model is used in the presence of high noise. We present analytical expressions
for this bias, which depends on the residual difference between the model and
real data. They can lead to biases not accounted for in previous calibration
schemes. By measuring the model bias, noise bias and their interaction, we
provide a complete statistical framework for measuring galaxy shapes with model
fitting methods from GRavitational lEnsing Accuracy Testing (GREAT) like
images. We demonstrate the noise and model interaction bias using a simple toy
model, which indicates that this effect can potentially be significant. Using
real galaxy images from the Cosmological Evolution Survey (COSMOS) we quantify
the strength of the model bias, noise bias and their interaction. We find that
the interaction term is often a similar size to the model bias term, and is
smaller than the requirements of the current and shortly upcoming galaxy
surveys.Comment: 11 pages, 3 figure
Controlling and leveraging small-scale information in tomographic galaxy-galaxy lensing
The tangential shear signal receives contributions from physical scales in
the galaxy-matter correlation function well below the transverse scale at which
it is measured. Since small scales are difficult to model, this non-locality
has generally required stringent scale cuts or new statistics for cosmological
analyses. Using the fact that uncertainty in these contributions corresponds to
an uncertainty in the enclosed projected mass around the lens, we provide an
analytic marginalization scheme to account for this. Our approach enables the
inclusion of measurements on smaller scales without requiring numerical
sampling over extra free parameters. We extend the analytic marginalization
formalism to retain cosmographic ("shear-ratio") information from small-scale
measurements that would otherwise be removed due to modeling uncertainties,
again without requiring the addition of extra sampling parameters. We test the
methodology using simulated likelihood analysis of a DES Year 5-like
galaxy-galaxy lensing and galaxy clustering datavector. We demonstrate that we
can remove parameter biases due to the presence of an un-modeled 1-halo
contamination of the galaxy-galaxy lensing signal, and use the shear-ratio
information on small scales to improve cosmological parameter constraints.Comment: 10 pages, 5 figure, submitted to MNRAS. Comments welcom
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