CROSS-CORRELATION WEAK LENSING OF SDSS GALAXY CLUSTERS. III. MASS-TO-LIGHT RATIOS

Abstract

We present measurements of the excess mass-to-light ratio (M/L) measured around MaxBCG galaxy clusters observed in the Sloan Digital Sky Survey. This red-sequence cluster sample includes objects from small groups with M200 ∼ 5 × 1012 h−1 M☉ to clusters with M200 ∼ 1015 h−1 M☉. Using cross-correlation weak lensing, we measure the excess mass density profile above the universal mean for clusters in bins of richness and optical luminosity. We also measure the excess luminosity density measured in the z = 0.25 i band. For both mass and light, we de-project the profiles to produce three-dimensional mass and light profiles over scales from 25 h−1 kpc to 22 h−1 Mpc. From these profiles we calculate the cumulative excess mass ΔM(r) and excess light ΔL(r) as a function of separation from the BCG. On small scales, where , the integrated mass-to-light profile (ΔM/ΔL)(r) may be interpreted as the cluster M/L. We find the (ΔM/ΔL)200, the M/L within r200, scales with cluster mass as a power law with index 0.33 ± 0.02. On large scales, where , the ΔM/ΔL approaches an asymptotic value independent of cluster richness. For small groups, the mean (ΔM/ΔL)200 is much smaller than the asymptotic value, while for large clusters (ΔM/ΔL)200 is consistent with the asymptotic value. This asymptotic value should be proportional to the mean M/L of the universe 〈M/L〉. We find 〈M/L〉b−2M/L = 362 ± 54h (statistical). There is additional uncertainty in the overall calibration at the ∼10% level. The parameter b2M/L is primarily a function of the bias of the L ≲ L* galaxies used as light tracers, and should be of order unity. Multiplying by the luminosity density in the same bandpass we find Ωmb−2M/L = 0.20 ± 0.03, independent of the Hubble parameter.