Formation of Galactic Halos from Seeded Hot Dark Matter

We study the formation of galactic halos in a flat universe dominated by massive neutrinos. The linear growth of a perturbation, seeded by a stationary point mass born at some arbitrarily early time in the early universe, is calculated fully relativistically. The nonlinear evolution of the perturbation is calculated using a dissipationless three- dimensional N-body code. We find that the halos generated are well approximated by isothermal spheres, generating flat rotation curves, in agreement with galactic rotational velocity observations. Further, it affirms the assumption used in the calculation of the Tremaine-Gunn limit. However, we find that with a massive object dominating the central region, the core radius becomes an ill-defined quantity, so with a large fraction of the inner region made up of some other material, such as baryons, it is possible to produce small galaxies with low velocity dispersions. With a system largely dominated by neutrinos, the simulations indicate the Tremaine-Gunn limit is overly conservative. In the case studied, the core radius was 50% larger and the central density about 3 times smaller than that given by the Tremaine & Gunn calculation.