Statistics of Physical Properties of Dark Matter Clusters
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Abstract
We have identified over 2000 well resolved cluster halos, and also their associated bound subhalos, from the output of a 1024^3 particle cosmological N-body simulation (of box size 320 h^-1 Mpc and softening length 3.2 h^-1 kpc). This has allowed us to measure halo quantities in a statistically meaningful way, and for the first time analyse their distribution for a large and well resolved sample. We characterize each halo in terms of its morphology, concentration, spin, circular velocity and the fraction of their mass in substructure. We also identify those halos that have not yet reached a state of dynamical equilibrium using the virial theorem with an additional correction to account for the surface pressure at the boundary. These amount to 3.4% of our initial sample. For the virialized halos, we find a median of 5.6% of halo mass is contained within substructure, with the distribution ranging between no identified subhalos to 65%. The fraction of mass in substructure increases with halo mass with logarithmic slope of 0.44 +- 0.06. Halos tend to have a prolate morphology, becoming more so with increasing mass. Subhalos have a greater orbital angular momentum per unit mass than their host halo. Furthermore, their orbital angular momentum is typically well aligned with that of their host. Overall, we find that dimensionless properties of dark matter halos do depend on their mass, thereby demonstrating a lack of self-similarity.