The evolution of dark matter halo profiles in a cosmological context

Environment has a significant impact on the evolution of dark halo profiles. We used a cosmological N-body simulation based on WMAP5 cosmology to study environmental effects on halo profiles. Host haloes located in sparse regions are highly concentrated, and more massive haloes have higher concentration index. This is because mass accretion affects only the outer part of the halo and consequently increase the virial radius having no effect on the scale radius. Conversely, host haloes located in dense regions have low concentration index. This is because frequent mergers affect even the inner part of the halo. So, scale radius increases with the growth of virial radius. Evolutions of subhalo profiles are essentially different from those of host haloes because subhaloes undergo tidal stripping. The stripping begins once a subhalo approaches closer than ~3 virial radii of the host halo. During the stripping, the inner part of the subhalo keep following NFW profile, but the mass of the outer part gradually decreases. As a result, when the subhalo reaches the pericenter of its host, only about inner 30% of the subhalo follows the NFW profile.