Testing Gravity with the Stacked Phase Space around Galaxy Clusters

TL;DR

This paper introduces a novel method combining galaxy redshift stacking and weak lensing to directly test gravity theories on large scales, promising significant improvements over current constraints.

Contribution

The paper proposes a new observational technique that uses stacked galaxy redshifts and lensing to measure the velocity field around clusters, enabling precise gravity tests.

Findings

Method can improve constraints on f(R) and DGP models by orders of magnitude.

Simulations show the technique's effectiveness with upcoming surveys.

Provides a direct test of gravity on 1-30 Mpc scales.

Abstract

In General Relativity, the average velocity field of dark matter around galaxy clusters is uniquely determined by the mass profile. The latter can be measured through weak lensing. We propose a new method of measuring the velocity field (phase space density) by stacking redshifts of surrounding galaxies from a spectroscopic sample. In combination with lensing, this yields a direct test of gravity on scales of 1-30 Mpc. Using N-body simulations, we show that this method can improve upon current constraints on f(R) and DGP model parameters by several orders of magnitude when applied to upcoming imaging and redshift surveys.