Assessing the accuracy of cosmological parameters estimated from velocity – density comparisons via simulations

Abstract

ABSTRACT A promising method for measuring the cosmological parameter combination fσ8 is to compare observed peculiar velocities with peculiar velocities predicted from a galaxy density field using perturbation theory. We use N-body simulations and semi-analytical galaxy formation models to quantify the accuracy and precision of this method. Specifically, we examine a number of technical aspects, including the optimal smoothing length applied to the density field, the use of dark matter haloes or galaxies as tracers of the density field, the effect of noise in the halo mass estimates or in the stellar-to-halo mass relation, and the effect of finite survey volumes. We find that for a Gaussian smoothing of $4 \mbox{$\, h^{-1}$}$ Mpc, the method has only small systematic biases at the level of 5 per cent. Cosmic variance affects current measurements at the 5 per cent level due to the volume of current redshift data sets.