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28 October 2008
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Tim Eifler (Bonn)
"Measuring Cosmic Shear with the Ring Statistics"
In recent years weak lensing by the large-scale structure of the
Universe, called cosmic shear, has become a valuable probe in
cosmology. Large upcoming surveys such as KIDS, Pan-STARRS, DES, SNAP,
and JDEM will improve the quality of cosmic shear data significantly,
enabling us to measure its signal with less than 1% statistical
error. In order to obtain cosmological parameters from these high
precision data properly, there remain issues to be addressed. On the
observational side, systematic errors, mainly from insufficient
PSF-correction, must be reduced, and a possible contribution to the
shear signal coming from intrinsic alignment or shape-shear
correlation must be excluded. On the theoretical side, we need
accurate predictions for P_delta(k) and precise statistical methods to
infer cosmological parameters. In this talk I review the basics of
cosmic shear focusing on the properties of its second-order
measures. I address the issue of E- and B-modes in the shear signal,
mention possible sources of B-mode contamination, and outline how to
separate E-modes from B-modes with the aperture mass dispersion. The
latter was improved by Schneider & Kilbinger (2006) who introduced the
so-called ring statistics. I explain advantages and problems of the
ring statistics, show how to optimize its signal-to-noise ratio, and
present the first shear signal measurement using the ring statistics
on data from the CFHTLS survey.
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