Properties of Cold Dark Matter Halos at z > 6

We compute the properties of dark matter halos with mass 10 − 10M⊙ at redshift z = 6 − 11 in the standard cold dark matter cosmological model, utilizing a very high resolution N-body simulation. We find that dark matter halos in these mass and redshift ranges are significantly biased over matter with a bias factor in the range 2− 6. The dark matter halo mass function displays a slope of 2.05±0.15 at the small mass end. We do not find a universal dark matter density profile. Instead, we find a significant dependence of the central density profile of dark matter halos on halo mass and epoch with α0 = 0.4 − 1.0; the high-mass (M ≥ 10M⊙) low-redshift (z ∼ 6) halos occupy the high end of the range and low-mass (M ∼ 10M⊙) high-redshift (z ∼ 11) halos occupy the low end. Additionally, for fixed mass and epoch there is a significant dispersion in α0 due to the stochastic assembly of halos. Our results fit a relationship of the form α0 = 0.75((1+ z)/7.0) (M/10M⊙) 0.11(1+z)/7.0 with a dispersion about this fit of ±0.5 and no systematic dependence of variance correlated with environment. The median spin parameter of dark matter halos is 0.03− 0.04 but with a large lognormal dispersion of ∼ 0.4. Various quantities are tabulated or fitted with empirical formulae. Subject headings: cosmology: theory—intergalactic medium—large-scale structure of universe—quasars: absorption lines Princeton University Observatory, Princeton University, Princeton, NJ 08544; [email protected] Princeton University Observatory, Princeton University, Princeton, NJ 08544; [email protected] Princeton University Observatory, Princeton University, Princeton, NJ 08544; [email protected] Princeton University Observatory, Princeton University, Princeton, NJ 08544; [email protected]; Institute for Astronomy, Cambridge University, Cambridge, England; [email protected]