We report the results of a cosmic shear survey using the 4.2-m William Herschel Telescope on La Palma, to a depth of R= 25.8 (z~ 0.8), over 4 deg2. The shear correlation functions are measured on scales from 1 to 15 arcmin, and are used to constrain cosmological parameters. We ensure that our measurements are free from instrumental systematic effects by performing a series of tests, including a decomposition of the signal into E- and B-modes. We also reanalyse the data independently, using the shear measurement pipeline developed for the COMBO-17 survey. This confirms our results and also highlights various effects introduced by different implementations of the basic `Kaiser-Squires-Broadhurst' shear measurement method. We find that the normalization of the matter power spectrum on 8h-1 Mpc scales is σ8= (1.02 +/- 0.15)(0.3/Ωm)1/2, where the 68 per cent confidence limit error includes noise, sample variance, covariance between angular scales, systematic effects, redshift uncertainty and marginalization over other parameters. We compare these results with other cosmic shear surveys and with recent constraints from the Wilkinson Microwave Anisotropy Probe experiment.
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- June 2005
- gravitational lensing;
- cosmology: observations;
- large-scale structure of Universe;
- 11 pages, 13 figures. Accepted version. Now includes a second, independent analysis of the WHT data using the COMBO-17 pipeline. This confirms our results, within statistical errors. A meticulous comparison of the two methods also highlights some important details of weak shear measurement for the first time