Testing Refracted Gravity with kinematics of galaxy clusters

TL;DR

This study tests Refracted Gravity, a classical gravity theory mimicking dark matter effects, using detailed galaxy cluster kinematic data, finding it comparable to Newtonian gravity but with inconsistencies in parameter universality.

Contribution

The paper applies an advanced kinematic analysis to galaxy clusters to constrain Refracted Gravity parameters, highlighting limitations and potential systematic effects.

Findings

RG describes cluster kinematics as well as Newtonian gravity but with a slight preference for the latter.

Different clusters require different RG parameters, challenging the universality assumption.

Systematic effects like deviations from spherical symmetry may influence parameter constraints.

Abstract

Refracted Gravity (RG) is a a classical theory of gravity where a gravitational permittivity $ a monotonically-increasing function of the local density rho , is introduced in the Poisson equation to mimic the effect of dark matter at astrophysical scales. We use high precision spectroscopic data of two massive galaxy clusters, MACS J1206.2-0847 at redshift z=0.44, and Abell S1063 (RXC J2248.7-4431) at z=0.35, to determine the total gravitational potential in the context of RG and to constrain the three, supposedly universal, free parameters of this model. Using an upgraded version of the MG-MAMPOSSt algorithm, we perform a kinematic analysis which combines the velocity distribution of the cluster galaxies and the velocity dispersion profile of the stars within the Brightest Cluster Galaxy (BCG). The unprecedented dataset used has been obtained by an extensive spectroscopic campaign carried out with the VIMOS and MUSE spectrographs at the ESO VLT. We found that RG describes the kinematics of these two clusters as well as Newtonian gravity, although the latter is slightly preferred. However, (i) each cluster requires a different set of the three free RG parameters, and (ii) the two sets are inconsistent with other results in the literature at different scales. We discuss the limitation of the method used to constrain the RG parameters as well as possible systematic effects which can give rise to the observed tension, notably deviations from the spherical symmetry and from the dynamical equilibrium of the clusters.