Galaxy Cluster Virial Masses and Omega

Abstract

The mean density of the universe is equal to the mass of a large galaxy cluster divided by the equivalent comoving volume in the field from which that mass originated. To reexamine the rich cluster {OMEGA}- value the CNOC Cluster Survey has observed 16 high X-ray luminosity clusters in the redshift range 0.17-0.55, obtaining approximately 2600 velocities in their fields. The systemic redshift, the rms line-of-sight velocity dispersion σ_1_, and the mean harmonic radius rnu_ are derived for each cluster using algorithms that correct for interlopers in redshift space and measure the angular extent of the sampling. The virial mass, and its internal error, are derived from σ_1_ and rnu_. The cluster luminosity is estimated from the K-corrected r-band luminosities of the cluster galaxies. Directly adding all the light to M_r_^K^ = - 18.5 mag, about 0.2L_sun_, and extrapolating for the small amount of light below the limit, the average mass-to-light ratio of the clusters is 295 +/- 53 h M_sun_ L_sun_^-1^, and the average mass per galaxy to M_r_^K^ = - 19.0 mag is 4.2 +/- 1.1 x 10^12^ h^-1^ M_sun_. The clusters are consistent with having a universal Mnu_/L-value (within the errors of about 25%) independent of their velocity dispersion, mean color of their galaxies, blue galaxy content, redshift, or mean interior density. Using field galaxies within the same data set, with the same corrections, we find that the closure mass-to-light ratio, ρ_c_/j, is 1025 +/- 140 h M_sun_ L_sun_^-1^, and the closure mass per galaxy to M_r_^K^ = - 19.0 mag, ρ_c_/{PHI} is 15.5 +/- 3.0 x 10^12^ h^-1^ M_sun_. Under the assumptions that the galaxies are distributed like the mass and that the galaxy luminosities and numbers are statistically conserved, assumptions that these data indirectly support, {OMEGA}_0_ = 0.24 +/- 0.05 +/- 0.09, where the errors are, respectively, the 1 σ random error and an estimate of the possible systematic error resulting from the normalization to galaxy content.