Omegaₘ and the CNOC Surveys

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The CNOC1 cluster survey measures Omegaₘ via Oort's method, Omegaₘ= M/L x j/rhoc, where M/L is the field mass-to-light ratio, j is the field luminosity density and rhoc is the closure density. A wide range of potential systematic effects are explicitly controlled by independently deriving the mean cluster mass profile (finding good agreement with theoretical predictions), the cluster light profile, the redshift evolution of both cluster and field galaxies, the differential evolution between the two, and the field and cluster efficiencies for the conversion of baryons into galaxies. We conclude that Omegaₘ=0.19+/-0.06 where the errors are objectively evaluated via resampling methods. The redshift evolution of the numbers of clusters per unit co-moving volume over the 0< z < 0.6 range is found to be very slow, as is required for consistency with a low density universe. The evolution of galaxy clustering in the field is compatible with a low density universe, and strongly disfavors models of galaxy evolution that associate low density halos with individual galaxies.