Results of a previous analysis of collisions between two galaxies near the center of a dense cluster of galaxies are applied to clusters as a whole. Effects of collisions on the galaxies within a dense cluster are analyzed for the cases of evolution of a homogeneous cluster of equal-mass galaxies, evolution of a test galaxy on a fixed background, and evolution of a cluster mass distribution. The debris hypothesis for the formation of cD galaxies is examined critically, and the suggestion that clusters of galaxies form a density or a dynamical age distribution is discussed. It is concluded that: (1) galaxies with velocity dispersions of about 180 km/s and radii of 100 pc or more suffer substantial changes due to collisions in the centers of dense clusters; (2) if all the mass at the center of a dense cluster is initially contained in isothermal galaxies with normal velocity dispersions, 90% of that mass will be liberated in a Hubble time; (3) the internal velocity dispersions of the galaxies should decrease by a factor of two; (4) predictions of the debris hypothesis appear to be generally in agreement with observations; and (5) Oemler's (1974) classification scheme is a dynamical age sequence.
D. O. Richstone (Mon,) studied this question.