Dwarf Dark Matter Halos

We use N-body simulations to study properties of dwarf halos with virial masses in the range 10 − 10hM⊙. Unlike recent reported results, we find that the density profiles of relaxed dwarf halos are well fitted by the NFW profile and do not have cores. 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. (2001a). We predict that present-day isolated dwarf halos should have a very large median concentration of ∼ 35. For halos with masses that range from 4.6× 10hM⊙ to 10 hM⊙ we measure the subhalo circular velocity function and find that they are similar when normalized to the circular velocity of the parent halo. 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. The 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