Measurement of the Bias Parameter from Weak Lensing

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Abstract
We have measured the correlation between the lensing signal induced by (dark) matter and the number counts of galaxies on scales ranging from 0.15 to 3.0 h Mpc (which correspond to aperture radii of 1'-15'). This provides a direct probe of the scale dependence of the ratio of the classical bias parameter b and the galaxy-mass correlation coefficient r. The results presented here are based on 16 deg2 of RC-band data taken with the Canada-France-Hawaii Telescope as part of the Red-Sequence Cluster Survey. We used a sample of lens galaxies with 19.5 < RC < 21 and a sample of source galaxies with 21.5 < RC < 24. The results are consistent with a scale-independent value of b/r, which provides valuable constraints on models of galaxy formation on scales that can only be probed through weak lensing. For the currently favored cosmology (Ωm = 0.3, ΩΛ = 0.7), we find that b/r = 1.05, similar to what is found on larger scales (~10 h Mpc) from local dynamical estimates. These results support the hypothesis that light traces mass on scales ranging from 0.15 out to ~10 h Mpc. The accuracy of the measurement will improve significantly in the coming years, enabling us to measure both b and r separately as a function of scale.
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