Mapping Growth and Gravity with Robust Redshift Space Distortions

TL;DR

This paper evaluates the robustness of redshift space distortion models for measuring cosmic growth, finding biases in common approaches and proposing a new fitting function for improved accuracy at smaller scales.

Contribution

It compares perturbation theory models to simulations, identifies biases in standard formulas, and introduces a new fitting function for better modeling of redshift space power spectra.

Findings

Kaiser formula biases growth rate estimates at k > 0.07 h/Mpc

Perturbation theory approaches can introduce 1-sigma biases

A new fitting function improves modeling accuracy at higher k

Abstract

Redshift space distortions caused by galaxy peculiar velocities provide a window onto the growth rate of large scale structure and a method for testing general relativity. We investigate through a comparison of N-body simulations to various extensions of perturbation theory beyond the linear regime, the robustness of cosmological parameter extraction, including the gravitational growth index, \gamma. We find that the Kaiser formula and some perturbation theory approaches bias the growth rate by 1-sigma or more relative to the fiducial at scales as large as k > 0.07 h/Mpc. This bias propagates to estimates of the gravitational growth index as well as \Omega_m and the equation of state parameter and presents a significant challenge to modelling redshift space distortions. We also determine an accurate fitting function for a combination of line of sight damping and higher order angular dependence that allows robust modelling of the redshift space power spectrum to substantially higher k.