Groups of Galaxies. 111. Mass-To Ratios and Crossing Times

Virial mass-to-light ratios and various crossing times are computed for 39 groups of galaxies identified in the first paper of this series. A typical group in the sample has five members and three measured radial velocities. Some of the groups may be plausibly modified or broken up into subgroups in order to remove contaminating foreground or background objects. Statistical evaluations of these data lead to the following conclusions: The most unbiased and crudest estimator of MIL gives 140 M0/L0. A more careful analysis indicates that, for rich clusters, MIL 200 M0/L0, while 65 M0./L0 is more appropriate for small groups. This implies an overall mean MIL 90 M4Lo., corresponding to 0.06. The group crossing times are typically one-tenth of the Hubble time, indicating that collapse and virialization have been completed recently. The density enhancements of the groups relative to the mean density in the Universe are roughly a factor of l0 . More and better radial-velocity data are badly needed for these groups. Subject headings: cosmology - galaxies: clusters of - galaxies: general - galaxies: redshifts - mass-luminosity relation