Estimates of cluster masses in screened modified gravity

TL;DR

This paper investigates how screened modified gravity models affect galaxy cluster mass estimates using simulations and observational data, revealing that different mass measurement methods probe different scalar field couplings and can constrain deviations from general relativity.

Contribution

It introduces a novel analysis of cluster mass estimates under models with non-universal scalar couplings and applies this to observational data to constrain modified gravity theories.

Findings

X-ray mass estimates are sensitive to baryon coupling

Kinematic mass estimates are sensitive to dark matter coupling

Constraints on deviations from general relativity are obtained from observational data

Abstract

We use cosmological hydrodynamical simulations to study the effect of screened modified gravity models on the mass estimates of galaxy clusters. In particular, we focus on two novel aspects: (i) we study modified gravity models in which baryons and dark matter are coupled with different strengths to the scalar field, and, (ii) we put the simulation results into the greater context of a general screened-modified gravity parametrization. We have compared the mass of clusters inferred via lensing versus the mass inferred via kinematical measurements as a probe of violations of the equivalence principle at Mpc scales. We find that estimates of cluster masses via X-ray observations is mainly sensitive to the coupling between the scalar degree of freedom and baryons - while the kinematical mass is mainly sensitive to the coupling to dark matter. Therefore, the relation between the two mass estimates is a probe of a possible non-universal coupling between the scalar field, the standard model fields, and dark matter. Finally, we used observational data of kinetic, thermal and lensing masses to place constraints on deviations from general relativity on cluster scales for a general parametrization of screened modified gravity theories which contains $f(R)$ and Symmetron models. We find that while the kinematic mass can be used to place competitive constraints, using thermal measurements is challenging as a potential non-thermal contribution is degenerate with the imprint of modified gravity.