The Average Mass and Light Profiles of Galaxy Clusters

The systematic errors in the virial mass-to-light ratio, M_v/L, of galaxyclusters as an estimator of the field M/L value are assessed. We overlay 14clusters in redshift space to create an ensemble cluster which averages oversubstructure and asymmetries. The combined sample, including background,contains about 1150 galaxies, extending to a projected radius of about twicer_200. The radius r_200, defined as where the mean interior density is 200times the critical density, is expected to contain the bulk of the virializedcluster mass. The dynamically derived M(r_200)/L(r_200) of the ensemble is0.82+/-0.14 . The M_v/L overestimate is attributed to not taking intoaccount the surface pressure term in the virial equation. Under the assumptionthat the velocity anisotropy parameter is in the range 0<=\beta<=2/3, thegalaxy distribution accurately traces the mass profile beyond about the central0.3r_200. There are no color or luminosity gradients in the galaxy populationbeyond 2r_200, but there is 0.11+/-0.05 mag fading in the r band luminositiesbetween the field and cluster galaxies. We correct the cluster virialmass-to-light ratio, M_v/L=289+/-50 h\msun/\lsun (calculated assuming q_0=0.1),for the biases in M_v and mean luminosity to estimate the field M/L=213+/-59h\msun/\lsun. With our self-consistently derived field luminosity density,j/\rho_c=1136+/-138 h\msun/\lsun (at z~1/3), the corrected M/L indicates\Omega_0=0.19+/-0.06+/-0.04 (formal 1\sigma random error and estimatedpotential systematic errors).