Angular momentum alignment of dark matter haloes

Using high-resolution cosmological N-body simulations, we investigate the tendency of dark matter haloes to have their axes of rotation aligned similarly to those of their neighbours, or pointing towards local large-scale structures. We quantify these effects as a function of scale using measures somewhat analogous to the velocity dispersion and infall velocity statistics. We find a weak mutual alignment between haloes of separation ∼1 h−1 Mpc. More interestingly, we measure a slight (one per cent), but highly significant trend for angular momentum vectors to point towards overdensities in the halo distribution field over the range 1–30 h−1 Mpc, i.e. up to the largest scales reliably probed by our simulations. We investigate the dependence of the observed correlations on cosmology, halo size, and redshift, and discuss the possibility of being able to observe such effects with real galaxy surveys.