Cluster Dynamics and Cluster Masses

In spite of the promise of new techniques for constraining the mass distribution in galaxy clusters, much remains to be learned from galaxy orbital velocities. This article reviews the theory of potential estimation in hot dynamical systems like galaxy clusters. An analysis is presented of the Coma cluster, based on a sample of 1500 galaxies with probable membership, of which 450 have measured velocities. The Coma data are shown to be consistent with a model in which the dark matter density falls roughly as r 3 inside of 1.5 Mpc (H 0 = 50), with, perhaps, a transition to a slower falloo at larger radii. We nd no signiicant evidence for a core in either the galaxy number densities or the mass distribution.