No need for dark matter in galaxy clusters within Galileon theory

TL;DR

This paper investigates whether a modified gravity model within the Galileon framework can explain galaxy cluster observations without invoking dark matter, showing that it can match data and differ statistically from general relativity.

Contribution

It demonstrates that an extended Galileon model can account for galaxy cluster lensing data without dark matter, providing new bounds on model parameters and challenging GR assumptions.

Findings

Model matches cluster observations without dark matter.

Excludes GR limit at 2σ confidence level for some parameters.

Provides bounds on Galileon model parameters.

Abstract

Modified gravity theories with a screening mechanism have acquired much interest recently in the quest for a viable alternative to General Relativity on cosmological scales, given their intrinsic property of being able to pass Solar System scale tests and, at the same time, to possibly drive universe acceleration on much larger scales. Here, we explore the possibility that the same screening mechanism, or its breaking at a certain astrophysical scale, might be responsible of those gravitational effects which, in the context of general relativity, are generally attributed to Dark Matter. We consider a recently proposed extension of covariant Galileon models in the so-called "beyond Horndeski" scenario, where a breaking of the Vainshtein mechanism is possible and, thus, some peculiar observational signatures should be detectable and make it distinguishable from general relativity. We apply this model to a sample of clusters of galaxies observed under the \textit{CLASH} survey, using both new data from gravitational lensing events and archival data from X-ray intra-cluster hot gas observations. In particular, we use the latter to model the gas density, and then use it as the only ingredient in the matter clusters' budget to calculate the expected lensing convergence map. Results show that, in the context of this extended Galileon, the assumption of having only gas and no Dark Matter at all in the clusters is able to match observations. We also obtain narrow and very interesting bounds on the parameters which characterize this model. In particular, we find that, at least for one of them, the general relativity limit is excluded at $2\sigma$ confidence level, thus making this model clearly statistically different and competitive with respect to general relativity.