Determination of the large scale volume weighted halo velocity bias in simulations

Understand

A profound assumption in peculiar velocity cosmology is $b_v=1$ at sufficiently large scales, where $b_v$ is the volume weighted halo(galaxy) velocity bias with respect to the matter velocity field.

• However, this fundamental assumption has not been robustly verified in numerical simulations.
• Furthermore, it is challenged by structure formation theory (BBKS, 1986, ApJ; Desjacques and Sheth, 2010, PRD), which predicts the existence of velocity bias (at least for proto-halos) due to the fact that halos reside in special regions (local density peaks).
• The major obstacle to measure the volume weighted velocity from N-body simulations is an unphysical sampling artifact.