Constraints on Ωm and Σ8 from Weak Lensing in Rcs Fields

We have analysed 53 square degrees of RC -band imaging data from the Red-Sequence Cluster Survey (RCS), and measured the excess correlations in the shapes of galaxies on scales out to ∼ 1.5 degrees. We separate the signal into an “E”(lensing) and “B”-mode (systematics), which allows us to study residual systematics. On scales larger than 10 arcminutes, we find no “B”-mode, suggesting that the signal at those scales is solely caused by gravitational lensing. On smaller scales we find a small, but significant “B”-mode. This signal is also present when we select a sample of bright (20 < RC < 22) galaxies. These galaxies are rather insensitive to observational distortions, and we therefore conclude that the oberved “B”-mode is likely to be caused by intrinsic alignments. To minimize the effect of intrinsic alignments, we limit the cosmic shear analysis to galaxies with 22 < RC < 24. We derive joint constraints on Ωm and σ8, by marginalizing over Γ, ΩΛ and the source redshift distribution, using different priors. Marginalizing over Γ and ΩΛ, and using a flat prior for the source redshift distribution, yields a conservative constraint of σ8 = 0.45 +0.09 −0.12Ω −0.55 m (95% confidence). A better constraint is derived when we use Gaussian priors for Γ (from the 2dF survey) and Ωm+ΩΛ (from CMB), and the source redshift distribution. For this choice of priors, we find σ8 = (0.46 +0.05 −0.07)Ω −0.52 m (95% confidence). We also investigated whether the RCS data can be used to constrain Γ. Using our set of Gaussian priors, we find that we can only place a lower bound on Γ for which we find Γ > 0.1+0.16Ωm (95% confidence). Comparison of the RCS results with three other recent cosmic shear measurements shows excellent agreement. The current weak lensing results are also in good agreement with CMB measurements, when we allow the reionization optical depth τ and the spectral index ns to vary. We present a simple demonstration of how the weak lensing results can be used as a prior in the parameter estimation from CMB measurements to derive constraints on the reionization optical depth τ . Subject headings: cosmology: observations − dark matter − gravitational lensing