2004AJ....128.1078R

CAIRNS (Cluster and Infall Region Nearby Survey) is a spectroscopic survey of the infall regions surrounding nine nearby rich clusters of galaxies. In our previous paper, we used redshifts within ∼10 h^–1 Mpc of the centers of the clusters to determine the mass profiles of the clusters based on the phase-space distribution of the galaxies. Here, we use Two Micron All Sky Survey photometry and an additional 515 redshifts to investigate the environmental dependence of near-infrared mass-to-light ratios. In the virial regions, the halo occupation function is nonlinear; the number of bright galaxies per halo increases more slowly than the mass of the halo. On larger scales, the light contained in galaxies is less clustered than the mass in rich clusters. Specifically, the mass-to-light ratio inside the virial radius is a factor of 1.8±0.3 larger than that outside the virial radius. This difference could result from changing fractions of baryonic to total matter or from variations in the efficiency of galaxy formation or disruption with environment. The average mass-to-light ratio M/L_K=53±5h implies Ω_m=0.18±0.03 (statistical) using the luminosity density based on Two Degree Field Galaxy Redshift Survey data. These results are difficult to reconcile with independent methods that suggest higher Ω_m. Reconciling these values by invoking bias requires that the typical value of M/L_Kchanges significantly at densities of ≲3ρ_c.