Pairwise velocities of dark matter haloes: a test for the Λ cold dark matter model using the bullet cluster

The existence of a bullet cluster (such as 1E 0657-56) poses a challenge to the concordance ? cold dark matter (?CDM) model. Here we investigate the velocity distribution of dark matter (DM) halo pairs in large N-body simulations with differing box sizes (250 h-1 Mpc Gpc) and resolutions. We examine various basic statistics such as the halo masses, pairwise halo velocities (v12), collisional angles and pair separation distances. We then compare our results to the initial conditions required to reproduce the observational properties of 1E 0657-56 in non-cosmological hydrodynamical simulations.