Complementarity of Peculiar Velocity Surveys and Redshift Space Distortions for Testing Gravity

TL;DR

This paper explores how combining peculiar velocity surveys with redshift space distortion measurements enhances testing gravity and constraining the growth rate of cosmic structures, especially at low redshifts.

Contribution

It demonstrates the benefits of integrating low-redshift peculiar velocity data with high-redshift clustering surveys to improve gravity tests and cosmological parameter constraints.

Findings

Peculiar velocity surveys can constrain $f\sigma_8$ to a few percent at $z\lesssim0.2$.

Combining surveys can determine the gravitational growth index with $\sigma(\gamma)\approx0.02$.

Survey characteristics and model assumptions affect the complementarity and precision of combined measurements.

Abstract

Peculiar-velocity surveys of the low-redshift universe have significant leverage to constrain the growth rate of cosmic structure and test gravity. Wide-field imaging surveys combined with multi-object spectrographs (e.g. ZTF2, LSST, DESI, 4MOST) can use Type Ia supernovae as informative tracers of the velocity field, reaching few percent constraints on the growth rate $f\sigma_8$ at $z\lesssim0.2$ where density tracers cannot do better than $\sim10\%$. Combining the high-redshift DESI survey mapping redshift space distortions with a low-redshift supernova peculiar velocity survey using LSST and DESI can determine the gravitational growth index to $\sigma(\gamma)\approx0.02$, testing general relativity. We study the characteristics needed for the peculiar velocity survey, and how its complementarity with clustering surveys improves when going from a $\Lambda$CDM model assumption to a $w_0$-$w_a$ cosmology.