Anisotropic mergers at high redshifts: the formation of cD galaxies and powerful radio sources

A new dynamical model for the formation of dominant cluster galaxies and powerful radio sources at high redshifts is proposed. In this model, powerful high-redshift radio galaxies are assumed to represent an early stage in the formation of massive cD galaxies in the centres of rich clusters, corresponding to an epoch when these galaxies were being built via mergers of smaller gas-rich protogalactic units. It is argued that in many cosmogonies such mergers will not occur haphazardly, but rather will proceed in a coherent or 'organized' manner along preferred axes which are related to large-scale anisotropies in the primordial density field. As a consequence of this anisotropic formation process, these galaxies are quite prolate in shape and have a built-in 'memory' of their surroundings, even at high redshifts. Such a formation scenario can account quite naturally for the observed shapes and kinematics of cD galaxies today, as well as their tendency to be aligned with the major axis of their parent cluster and the galaxy distribution on much larger scales.