ar X iv : a st ro - p h / 03 08 34 8 v 2 1 1 M ay 2 00 4 Dwarf Dark Matter Halos

We study properties of dark matter halos at high redshifts z = 2−10 for a vast range of masses with the emphasis on dwarf halos with masses 10−10hM⊙. We find that the density profiles of relaxed dwarf halos are well fitted by the NFW profile and do not have cores. We compute the halo mass function and the halo spin parameter distribution and find that the former is very well reproduced by the Sheth & Tormen model while the latter is well fitted by a lognormal distribution with λ0 = 0.042 and σλ = 0.63. We estimate the distribution of concentrations for halos in mass range that covers six orders of magnitude from 10 hM⊙ to 10 13 hM⊙, and find that the data are well reproduced by the model of Bullock et al. The extrapolation of our results to z = 0 predicts that present-day isolated dwarf halos should have a very large median concentration of ∼ 35. We measure the subhalo circular velocity functions for halos with masses that range from 4.6× 109h−1M⊙ to 10 h−1M⊙ and find that they are similar when normalized to the circular velocity of the parent halo. Dwarf halos studied in this paper are many orders of magnitude smaller than well-studied clusterand Milky Way-sized halos. Yet, in all respects the dwarfs are just down-scaled versions of the large halos. They are cuspy and, as expected, more concentrated. They have the same spin parameter distribution and follow the same mass function that was measured for large halos. Subject headings: cosmology: theory — cosmology: dark matter — galaxies: formation — galaxies: halos — methods: numerical