Cosmological constraints from the 100‐deg 2 weak‐lensing survey ★

We present a cosmic shear analysis of the 100‐deg 2 weak‐lensing survey, combining data from the CFHTLS‐Wide, RCS, VIRMOS‐DESCART and GaBoDS surveys. Spanning ∼100 deg 2 , with a median source redshift z ∼ 0.78 , this combined survey allows us to place tight joint constraints on the matter density parameter Ω m , and the amplitude of the matter power spectrum σ 8 , finding σ 8 (Ω m /0.24) 0.59 = 0.84 ± 0.05 . Tables of the measured shear correlation function and the calculated covariance matrix for each survey are included as supplementary material to the online version of this article. The accuracy of our results is a marked improvement on previous work owing to three important differences in our analysis; we correctly account for sample variance errors by including a non‐Gaussian contribution estimated from numerical simulations; we correct the measured shear for a calibration bias as estimated from simulated data; we model the redshift distribution, n ( z ) , of each survey from the largest deep photometric redshift catalogue currently available from the CFHTLS‐Deep. This catalogue is randomly sampled to reproduce the magnitude distribution of each survey with the resulting survey‐dependent n ( z ) parametrized using two different models. While our results are consistent for the n ( z ) models tested, we find that our cosmological parameter constraints depend weakly (at the 5 per cent level) on the inclusion or exclusion of galaxies with low‐confidence photometric redshift estimates ( z > 1.5) . These high‐redshift galaxies are relatively few in number but contribute a significant weak‐lensing signal. It will therefore be important for future weak‐lensing surveys to obtain near‐infrared data to reliably determine the number of high‐redshift galaxies in cosmic shear analyses.