An Enlarged Cosmic Shear Survey with the William Herschel Telescope

We report the results of a cosmic shear survey using the 4.2m William Herschel Telescope on La Palma, to a depth of R=25.8 (z~0.8), over 4 square degrees. The shear correlation functions are measured on scales from 1' to 15', and are used to constrain cosmological parameters. We ensure that our measurements are free from instrumental systematics 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 "KSB" shear measurement method. We find that the normalisation of the matter power spectrum on 8 h^{-1}Mpc scales is sigma_8=(1.02+/-0.15)(0.3/Omega_m)^{0.5}, where the 68%CL error includes noise, sample variance, covariance between angular scales, systematic effects, redshift uncertainty and marginalisation over other parameters. We compare these results with other cosmic shear surveys and with recent constraints from the WMAP experiment.