Large-scale anisotropies on halo infall

Abstract

We perform a statistical analysis of the peculiar velocity field around darkmatter haloes in numerical simulations. We examine different properties of theinfall of material onto haloes and its relation to central halo shapes and theshape of the large scale surrounding regions (LSSR).We find that the amplitude of the infall velocity field along the halo shapeminor axis is larger than that along the major axis. This is consistent forgeneral triaxial haloes, and for both prolate and oblate systems. We alsoreport a strong anisotropy of the velocity field along the principal axes ofthe LSSR.The infall velocity field around dark matter haloes reaches a maximum valuealong the direction of the minor axis of the LSSR, whereas along the directionof its major axis, it exhibits the smallest velocities. We also analyse thedependence of the matter velocity field on the local environment. The amplitudeof the infall velocity at high local density regions is larger than at lowlocal density regions. The velocity field tends to be more laminar along thedirection towards the minor axis of the LSSR, where the mean ratio between flowvelocity and velocity dispersion is of order unity and nearly constant up toscales of 15 Mpc h$^{-1}$.We also detect anisotropies in the outflowing component of the velocity field,showing a maximum amplitude along the surrounding LSSR major axis.