Dynamical friction in aspherical clusters
This paper investigates the way the morphologies of rich clusters of galaxies will be affected by the action of dynamical friction on the brighter galaxies. It is argued that rich clusters, which are often elongated on the sky although not rotating, owe their shapes to frozen-in velocity anisotropy. A calculation shows that if the velocity distributions of these clusters are anisotropic, the anisotropy of the distributions of the brighter galaxies will be increased by the action of dynamical friction. The time scale for the operation of this effect is precisely the time scale for the action of dynamical friction in spherical clusters. We do not know, however, what this timescale is because we are uncertain how large are the (M/L) values of bright galaxies. I review the evidence that the distributions of bright galaxies in several clusters are more elongated on the sky than the distributions of less bright galaxies. Application of these ideas to the formation of cD galaxies and the capture of globular clusters by galactic nuclei is discussed.