Large-scale intrinsic alignments of dark matter halo orientations with velocity field

Apr 29, 2019 - 11:00 am to 12:00 pm

Campus, Varian 355

Teppei Okumura (ASIAA)

The kinematic Sunyaev-Zel'dovich effect enables us to directly probe the density-weighted velocity field up to very large cosmic scales. We investigate the effects of intrinsic alignments (IA) of dark-matter halo shapes on cosmic density and velocity fields on such large scales. In literature IA have been detected with the halo density field up to ~ 100 Mpc/h both in simulations and observations. In this paper we introduce the corresponding various velocity statistics, the (density-weighted) velocity-intrinsic ellipticity (VI) correlation, angle-binned pairwise infall momentum and momentum correlation function. We derive theoretical expressions for these velocity alignment statistics for the first time based on the linear alignment model. Using large-volume, high-resolution N-body simulations, we measure the alignment statistics of density and velocity. Behaviors of IA in the velocity statistics are similar to those in the density statistics, except that the halo orientations are aligned with the velocity field up to scales larger than those with the density field, r > 100Mpc/h. We show that the detected IA of the velocity field can be well predicted by the linear alignment model. Our results indicate that observations of IA with the velocity field on large scales can provide additional information on cosmological models.