Profiles of dark haloes: evolution, scatter, and environment
Abstract
We study dark-matter halo density profiles in a high-resolution N-body simulation of an LCDM cosmology. Our statistical sample contains ~5000 haloes in the range 1011-1014 Msun. The profiles are parameterized by an NFW form with two parameters, an inner radius rs and a virial radius rv, and we define the halo concentration cv = rv/rs. First, we find that, for a given halo mass, the redshift dependence of the median concentration is cv ~ 1/(1+z), corresponding to a roughly constant rs with redshift. We present an improved analytic treatment of halo formation that fits the measured relations between halo parameters and their redshift dependence. The implications are that high-redshift galaxies are predicted to be more extended and dimmer than expected before. Second, we find that the scatter in log(cv) is ~0.18, corresponding to a scatter in maximum rotation velocities of dV/V ~ 0.12. We discuss implications for modelling the Tully-Fisher relation, which has a smaller reported intrinsic scatter. Third, haloes in dense environments tend to be more concentrated than isolated haloes. These results suggest that cv is an essential parameter for the theory of galaxy modelling, and we briefly discuss implications for the universality of the Tully-Fisher relation, the formation of low surface brightness galaxies, and the origin of the Hubble sequence.
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