Properties of Cold Dark Matter Halos at z>6
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We compute the properties of dark matter halos with mass $10^{6.5}-10^9\msun$ 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 $2.05\pm 0.15$ 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 $α_0=0.4-1.0$; the high-mass ($M\ge 10^8\msun$) low-redshift ($z\sim 6$) halos occupy the high end of the range and low-mass ($M\sim 10^{7}\msun$) high-redshift ($z\sim 11$) halos occupy the low end. Additionally, for fixed mass and epoch there is a significant dispersion in $α_0$ due to the stochastic assembly of halos. Our results fit a relationship of the form $α_0=0.75((1+z)/7.0)^{-1.25}(M/10^7\msun)^{0.11(1+z)/7.0}$ with a dispersion about this fit of $\pm 0.5$ 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 $\sim 0.4$. Various quantities are tabulated or fitted with empirical formulae.
38 pages, submitted to ApJ, name revised (the first author name was wrong)
38 pages, submitted to ApJ, name revised (the first author name was wrong)