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

Abstract

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 ΩM, the mass power spectrum normalisation σ8, the shape parameter Γ and the redshift of the sources zs. Constraints on ΩM and σ8 (resp. Γ and zs) are provided by marginalising over Γ and zs (resp. ΩM and σ8). For a flat ΛCDM cosmologies, using a photometric redshift prior for the sources and Γ ε [0.1,0.4], we find σ8 = (0.57 ± 0.04) ΩM(0.24 ± 0.18)ΩM-0.49 at the 68% confidence level (the error budget includes statistical noise, full cosmic variance and residual systematics). The estimate of Γ, marginalised over ΩM ε [0.1, 0.4], σ8 ε [0.7, 1.3] and zs constrained by photometric redshifts, gives Γ = 0.25 ± 0.13 at 68% confidence. Adopting h = 0.7, a flat universe, Γ = 0.2 and Ωm = 0.3 we find σ8 = 0.98 ± 0.06. Combined with CMB measurements, our results suggest a non-zero cosmological constant and provide tight constraints on ΩM and σ8. 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.