Measuring cosmic shear with the ring statistics
Abstract
Context. Commonly used methods of decomposing E and Bmodes in cosmic shear, namely the aperture mass dispersion and the E/Bmode shear correlation function, suffer from incomplete knowledge of the twopoint correlation function (2PCF) on very small and/or very large scales. The ring statistics, the most recently developed cosmic shear measure, improves on this issue and is able to decompose E and Bmodes using a 2PCF measured on a finite interval.
Aims: First, we improve on the ring statistics' filter function over the signaltonoise ratio (S/N). Second, we examine the ability of the ring statistics to constrain cosmology and compare the results to cosmological constraints obtained with the aperture mass dispersion. Third, we use the ring statistics to measure a cosmic shear signal from CFHTLS (CanadaFranceHawaii Telescope Legacy Survey) data.
Methods: We consider a scaledependent filter function for the ring statistics, which improves its S/N. To examine the information content of the ring statistics, we employed raytracing simulations and developed an expression of the ring statistics' covariance in terms of a 2PCF covariance. We performed a likelihood analysis with simulated data for the ring statistics in the σ_8 parameter space and compared the information content of ring statistics and aperture mass dispersion. Regarding our third aim, we used the 2PCF of the latest CFHTLS analysis to calculate the ring statistics and its error bars.
Results: Although the scaledependent filter function improves the S/N of the ring statistics, the S/N of the aperture mass dispersion is higher. In addition, we show that filter functions exist that decompose E and Bmodes using a finite range of 2PCFs (EBstatistics) and have higher S/N than the ring statistics. However, we find that data points of the latter are significantly less correlated than data points of the aperture mass dispersion and the EBstatistics. As a consequence the ring statistics is an ideal tool for identifying remaining systematics accurately as a function of angular scale. We use the ring statistics to measure a E and Bmode shear signal from CFHTLS data.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 January 2010
 DOI:
 10.1051/00046361/200912888
 arXiv:
 arXiv:0907.2320
 Bibcode:
 2010A&A...510A...7E
 Keywords:

 gravitational lensing: weak;
 largescale structure of Universe;
 methods: data analysis;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 10 pages, 5 figures, submitted to Astronomy and Astrophysics