Testing emergent gravity with mass densities of galaxy clusters

TL;DR

This study tests emergent gravity against galaxy cluster mass profiles using weak-lensing and x-ray data, finding that with systematic uncertainties, EG can fit observations, but it cannot be conclusively ruled out as an alternative to dark matter.

Contribution

The paper provides an empirical assessment of emergent gravity predictions using real cluster data, highlighting the importance of systematic uncertainties in testing gravity models.

Findings

EG fits cluster profiles near the virial radius

Systematic uncertainties can reconcile EG with observations

EG cannot be ruled out as an alternative to dark matter

Abstract

We use a sample of 23 galaxy clusters to test the predictions of emergent gravity (EG) as alternative to dark matter. Our sample has both weak-lensing inferred total mass profiles as well as x-ray inferred baryonic gas mass profiles. Using nominal assumptions about the weak-lensing and x-ray mass profiles, we find that the EG predictions (based on no dark matter) are acceptable fits only near the virial radius. In the cores and in the outskirts, the mass profile shape differences allow us to confirm previous results that the EG model can be ruled out at $>5\sigma$. However, when we account for systematic uncertainties in the observed weak-lensing and x-ray profiles, we find good agreement for the EG predictions. For instance, if the weak-lensing total mass profiles are shallow in the core and the x-ray gas density profiles are steep in the outskirts, EG can predict the observed dark matter profile in $0.3 \le r \le 1$R$_{200}$, where R$_{200}$ is the radius which encloses 200$\times$ the critical density of the Universe. The required x-ray and lensing shapes are within the current observational systematics-limited errors on cluster profiles. We also show that EG itself allows flexibility in its predictions, which can allow for good agreement between the observations and the predictions. We conclude that we cannot formally rule our EG as an alternative to dark matter on the cluster scale and that we require better constraints on the weak-lensing and gas mass profile shapes in the region $0.3 \le r \le 1$R$_{200}$.