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Paper: The Dark Matter Substructure of Clusters and Galaxies
Volume: 176, Observational Cosmology: The Development of Galaxy Systems
Page: 140
Authors: Ghigna, S.; Moore, B.; Governato, F.; Lake, G.; Quinn, T.; Stadel, J.
Abstract: We study the dark matter substructure of galaxies and clusters using high resolution N-body simulations of a cold dark matter universe. In units of the virial mass and the virial radius, our best mass and force resolutions are 3.5 × 10^{-7} and ~1.3 × 10^{-3} respectively. This allows us to identify up to 1500 substructure halos within the virial radius and to perform an unprecedented statistical study of the properties of halos that evolve in high density environments. A remarkable result is the similarity between the abundance of substructure on galactic and cluster scales. The cumulative fraction of mass attached to substructure halos is 12-14% and, in fully virialized systems, varies roughly linearly with the distance from the objects's center; it is ~0 at distances below 10% of the virial radius. The orbital distribution is close to isotropic and unbiased with respect to both position and the orbits of the smooth dark matter background; no velocity bias is detected. The median ratio of apocentric to pericentric radii is ~6:1. Substructure halos have tidal radii that generally agree with the simple analytic prediction applied to their orbital pericenters. Their concentrations are higher than those in the field (evidence of earlier formation). Their density profiles can be modified at all radii by tidal forces and individual encounters with other halos; mass loss through such heating processes can cause the circular velocities of massive halos to drop by as much as 25%. Mergers are very rare inside the virial radius.
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