Mass segregation and missing mass in the Coma cluster

Abstract

Earlier dynamical work is used to check the applicability of the conventional dynamical friction formula to clusters of galaxies. This work is then used to analyze the detailed distribution of galaxies in the Coma cluster, where mass segregation is confirmed to be weak. This lack of segregation is in strong contradiction with a numerical model in which the galaxies contain all the cluster mass, and it is inferred that only a small fraction of this mass can be attached to the individual galaxies. Arguments based on dynamical friction lead to an upper limit on the present mean mass-to-light ratio of the galaxies which is much less than the mass-to-light ratio of the cluster as a whole. The cluster must be bound by intergalactic material.