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

Abstract

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 Ω M , the mass power spectrum normalisation σ 8 , the shape parameter Γ and the redshift of the sources z s . Constraints on Ω M and σ 8 (resp. Γ and z s ) are provided by marginalising over Γ and z s (resp. Ω M and σ 8 ). For a flat ΛCDM cosmologies, using a photometric redshift prior for the sources and Γ ∈ [0.1, 0.4], we find σ 8 = (0.57 ± 0.04) Ω (0.24∓0.18)Ω M −0.49 M at the 68% confidence level (the error budget includes statistical noise, full cosmic variance and residual systematics). The estimate of Γ, marginalised over Ω M ∈ [0.1, 0.4], σ 8 ∈ [0.7, 1.3] and z s constrained by photometric redshifts, gives Γ = 0.25 ± 0.13 at 68% confidence. Adopting h = 0.7, a flat universe, Γ = 0.2 and Ω m = 0.3 we find σ 8 = 0.98 ± 0.06. Combined with CMB measurements, our results suggest a non-zero cosmological constant and provide tight constraints on Ω M and σ 8 . 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.

Current status of weak gravitational lensing

“…The most recent cosmic shear studies (Bacon et al, 2002;Hoekstra et al, 2002b;Refregier et al, 2002;Van Waerbeke et al, 2002) show excellent agreement. This is remarkable, given the fact that the data have been taken with different instruments, filters, and depths.…”

“…The result from Van Waerbeke et al (2002) might be biased high, because of their large scale "B"-mode. Both Bacon et al (2002) and Refregier et al (2002) do not separate their signal into "E" and "B'-modes, and therefore it might also include some residual systematics.…”

Intrinsic alignment-lensing interference as a contaminant of cosmic shear

“…It thus avoids the astrophysical complications involved in other means of measuring the matter distribution such as galaxy clustering. Recent first detections of the cosmic shear autopower spectrum [1][2][3][4][5][6][7][8] have stimulated proposals for more ambitious projects in the future, such as CFHTLS [9], Pan-STARRS [10], SNAP [11], and LSST [12], which aim for percent-level precision. Comparison of the shear power spectra at different redshifts and/or to the primordial fluctuation amplitude derived from cosmic microwave background (CMB) anisotropy measurements can constrain the cosmological growth factor and hence parameters such as the neutrino mass, amplitude of fluctuations 8 , and dark energy equation of state [13][14][15][16][17][18].…”

Sample Variance Considerations for Cluster Surveys

“…At the same time, independent constraints on mass-observable relations can, in principle, be obtained from weak lensing analyses of large X-ray-selected cluster samples. In addition, the power spectrum normalization at cluster scales can be obtained independently from studies of cosmic shear (e.g., Van Waerbeke et al 2002). Independent measurement of 8 would allow use of the local cluster temperature function to constrain the present-day M-T X relation.…”