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 of 10⁷-10⁹ h^-1 M_solar. We find that the density profiles of relaxed dwarf halos are well fitted by the Navarro, Frenk, & White (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 σ_λ=0.63. We estimate the distribution of concentrations for halos in a mass range that covers 6 orders of magnitude, from 10⁷ to 10¹³ h^-1 M_solar, 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 4.6×10⁹ to 10¹³ h^-1 M_solar 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 cluster- and Milky Way-sized halos. Yet, in all respects the dwarfs are just downscaled 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.