A Measurement of Weak Lensing by Large‐Scale Structure in Red‐Sequence Cluster Survey Fields

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Abstract
We have analyzed ~24 deg2 of RC-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'. We have used data from two different telescopes: ~16.4 deg2 of Canada-France-Hawaii Telescope data and ~7.6 deg2 of Cerro Tololo Inter-American Observatory 4 m 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 RC = 24, for which the redshift distribution is known relatively well. This allows us to constrain some cosmological parameters. For the currently favored ΛCDM model (Ωm = 0.3, ΩΛ = 0.7, Γ = 0.21), we obtain σ8 = 0.81 (95% confidence), in agreement with the 2001 results from Van Waerbeke and coworkers, who 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.
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