Beyond general relativity: probing gravity with gravitational redshifts

TL;DR

This paper explores how gravitational redshift measurements from galaxy clusters can test modifications to general relativity, emphasizing the importance of survey design and data quality for constraining alternative gravity theories.

Contribution

It develops an end-to-end pipeline to assess how survey parameters influence constraints on modified gravity using gravitational redshift data.

Findings

Wide-field spectroscopic surveys improve constraint precision.

High-purity stacking enhances measurement accuracy.

Controlling systematic effects is crucial for reliable results.

Abstract

Despite the success of general relativity (GR), the unexplained nature of dark energy on cosmological scales leaves open the question of whether GR provides a complete description of gravity. This quest is further motivated by growing tensions among cosmological observations when interpreted within $\Lambda$CDM. Gravitational redshifts of cluster member galaxies probe cluster potentials on megaparsec scales directly, complementing conventional large-scale structure tests. Here, we investigate how redshift precision and survey design propagate into constraints on modified gravity using an end-to-end pipeline run on mock catalogues, focusing on mis-centring and spectroscopic completeness. We find that competitive measurements require wide-field spectroscopic cluster surveys explicitly designed to maximise the number of spectroscopically confirmed members per cluster, to enable high-purity stacking, and to control systematic effects.