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

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 M(200) similar to 5 x 10(12) h(-1) M(circle dot) to clusters with M(200) similar to 10(15) h(-1) M(circle dot). Using cross-correlation weak lensing, we measure the excess mass density profile above the universal mean Delta rho(r) = rho(r) - (rho) over bar for clusters in bins of richness and optical luminosity. We also measure the excess luminosity density Delta l(r) = l(r) - (l) over bar 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 Delta M(r) and excess light Delta L(r) as a function of separation from the BCG. On small scales, where rho(r) >> (rho) over bar the integrated mass-to-light profile (Delta M/Delta L)(r) may be interpreted as the cluster M/L. We find the (Delta M/Delta L)(200), the M/L within r(200), scales with cluster mass as a power law with index 0.33 +/- 0.02. On large scales, where rho(r) similar to (rho) over bar the Delta M/Delta L approaches an asymptotic value independent of cluster richness. For small groups, the mean (Delta M/Delta L)(200) is much smaller than the asymptotic value, while for large clusters (Delta M/Delta L)(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(M/L)(-2) = 362 +/- 54h (statistical). There is additional uncertainty in the overall calibration at the similar to 10% level. The parameter b(M/L)(2) is primarily a function of the bias of the L less than or similar to L(*) galaxies used as light tracers, and should be of order unity. Multiplying by the luminosity density in the same bandpass we find Omega(m)b(M/L)(-2) = 0.20 +/- 0.03, independent of the Hubble parameter.