A measurement of weak lensing by large scale structure in RCS fields
Henk Hoekstra, Howard K. C. Yee, Michael D. Gladders, L. Felipe Barrientos, Patrick B. Hall, Leopoldo Infante
TL;DR
This paper measures cosmic shear from weak lensing by large-scale structure using ~24 deg^2 of RC-band data from the Red-Sequence Cluster Survey, comparing two independent instruments (CFHT and CTIO) to validate systematics. By modeling the top-hat variance of the shear and incorporating a well-characterized source redshift distribution, it constrains cosmological parameters and finds results consistent with a LambdaCDM universe, notably yielding sigma8 around 0.8. The analysis emphasizes rigorous PSF and camera distortion corrections, supported by simulations, and demonstrates the viability of cosmic shear as a cosmological probe with cross-instrument consistency. These results bolster confidence in weak lensing measurements and lay groundwork for tighter constraints with expanded photometric redshifts and intrinsic alignment analyses.
Abstract
We have analysed ~24 square degrees of R_C-band imaging data from the Red-Sequence Cluster Survey (RCS), and measured the excess correlations between galaxy ellipticities on scales ranging from 1 to 30 arcminutes. We have used data from two different telescopes: ~16.4 square degrees of CFHT data and ~7.6 square degrees of CTIO 4-meter data, distributed over 13 widely separated patches. For the first time, a direct comparison can be made of the lensing signal measured using different instruments, which provides an important test of the weak lensing analysis itself. The measurements obtained from the two telescopes agree well. For the lensing analysis we use galaxies down to a limiting magnitude of R_C=24, for which the redshift distribution is known relatively well. This allows us to constrain some cosmological parameters. For the currently favored $Λ$CDM model $(Ω_m=0.3, Ω_Λ=0.7, Γ=0.21)$ we obtain $σ_8=0.81^{+0.14}_{-0.19}$ (95% confidence), in agreement with the results from Van Waerbeke et al. (2001) which used fainter galaxies (and consequently higher redshift galaxies). The good agreement between these two very different weak lensing studies demonstrates that weak lensing is a useful tool in observational cosmology.