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

TL;DR

This study evaluates the accuracy of estimating cosmological parameters from velocity-density comparisons using simulations, focusing on technical factors affecting precision and bias.

Contribution

It provides a detailed analysis of the methodological uncertainties and biases in using velocity-density comparisons for cosmological parameter estimation.

Findings

Gaussian smoothing of 4 Mpc/h minimizes biases

Current measurements are affected by 5% cosmic variance

Method achieves small systematic biases with proper smoothing

Abstract

A promising method for measuring the cosmological parameter combination fsigma_8 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-analytic 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 halos 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 Mpc/h, the method has only small systematic biases at the level of 5%. Cosmic variance affects current measurements at the 5% level due to the volume of current redshift data sets.