Formation of cD Galaxies and Dissipationless Collapse
There is strong new evidence that first ranked galaxies are aligned with their parent cluster and with the direction of the nearest neighbour cluster (scale 15h -1Mpc) and that the average ellipticity of first ranked ellipticals is a strongly increasing function of radius. The alignment effect is limited to first ranked galaxies. In hierarchical clustering scenarios like the cold dark matter theory, galactic halos and clusters of galaxies are expected to have moderate asphericity. We present numerical results of a study of the dissipationless collapse of moderately aspherical systems. Our results indicate that the central part of the collapsed and virialized system does show the large scale elongation imposed by the initial conditions if the system is prolate. We also reproduce the increasing ellipticity as a function of radius that is observed for brightest cluster ellipticals.
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