paper

Cross-correlation Weak Lensing of SDSS Galaxy Clusters III: Mass-to-light Ratios

arXiv:0709.1162 · doi:10.1088/0004-637X/703/2/2232

Abstract

We present measurements of the excess mass-to-light ratio measured aroundMaxBCG galaxy clusters observed in the SDSS. This red sequence cluster sample includes objects from small groups with masses ranging from ~5x10^{12} to ~10^{15} M_{sun}/h. Using cross-correlation weak lensing, we measure the excess mass density profile above the universal mean Δρ(r) = ρ(r) - \barρ for clusters in bins of richness and optical luminosity. We also measure the excess luminosity density Δl(r) = l(r) - \bar{l} measured in the z=0.25 i-band. For both mass and light, we de-project the profiles to produce 3D mass and light profiles over scales from 25 kpc/ to 22 Mpc/h. From these profiles we calculate the cumulative excess mass M(r) and excess light L(r) as a function of separation from the BCG. On small scales, where ρ(r) >> \barρ, the integrated mass-to-light profile may be interpreted as the cluster mass-to-light ratio. We find the M/L_{200}, the mass-to-light ratio within r_{200}, scales with cluster mass as a power law with index 0.33+/-0.02. On large scales, where ρ(r) ~ \barρ, the M/L approaches an asymptotic value independent of cluster richness. For small groups, the mean M/L_{200} is much smaller than the asymptotic value, while for large clusters it is consistent with the asymptotic value. This asymptotic value should be proportional to the mean mass-to-light ratio of the universe <M/L>. We find <M/L>/b^2_{ml} = 362+/-54 h (statistical). There is additional uncertainty in the overall calibration at the ~10% level. The parameter b_{ml} 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 Ω_m/b^2_{ml} = 0.02+/-0.03, independent of the Hubble parameter.

Third paper in a series; v2.0 incorporates ApJ referee's suggestions

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