A DYNAMICAL STUDY OF FOUR ABELL CLUSTERS OF GALAXIES

Abstract

A dynamical study of the four Abell clusters of galaxies A154, A407, A671, and Al 185 is presented. These are all regular clusters of galaxies with low Abell richness classifications and low X-ray luminosities. New photometric and spectroscopic data are reported. These have been augmented by previously existing redshift measurements for these clusters. Total cluster luminosities and masses (virial and projected) are estimated. Available X-ray data for these clusters are used to estimate total cluster masses assuming that the intracluster gas is isothermal. All three mass estimates are found to be in good agreement for the four clusters studied here. Although the virial mass estimates measured here are reliable only if galaxies trace the cluster mass distribution, the other two mass estimations do not require this. It is argued that the good agreement of these independent mass estimates is consistent with the hypothesis that light traces mass. aJiv/L values are determined for the four clusters. They imply that the dark component of these clusters comprises ~ 90% of the total cluster masses. If cluster 9JI/L values are representative of the universe as a whole, a value of 0.2 < I1 < I is implied. Although these values do not favor closure, they do suggest that much of the dark matter present in the universe is nonbaryonic in nature.