Likelihood analysis of cosmic shear on simulated and VIRMOS-DESCART data

We present a maximum likelihood analysis of cosmological parameters from measurements of the aperture mass up to 35 arcmin using simulated and real cosmic shear data. A four-dimensional parameter space is explored which examines the mean density , the mass power spectrum normalisation , the shape parameter Γ and the redshift of the sources zs. Constraints on and (resp. Γ and zs) are provided by marginalising over Γ and zs ( resp. and ). For a flat ΛCDM cosmologies, using a photometric redshift prior for the sources and , we find at the confidence level (the error budget includes statistical noise, full cosmic variance and residual systematics). The estimate of Γ, marginalised over , and zs constrained by photometric redshifts, gives at confidence. Adopting , a flat universe, and we find . Combined with CMB measurements, our results suggest a non-zero cosmological constant and provide tight constraints on and . Finally, we compare our results to the cluster abundance ones, and discuss the possible discrepancy with the latest determinations of the cluster method. In particular we point out the actual limitations of the mass power spectrum prediction in the non-linear regime, and the importance in improving this.