The role of Dark Matter sub-halos in the non-thermal emission of galaxy clusters

TL;DR

This study demonstrates that incorporating observed dark matter sub-halos into models of galaxy clusters improves the match between predicted and observed non-thermal radio emissions, making dark matter a viable explanation for radio halos.

Contribution

It introduces a novel approach by including observed DM sub-halos in the modeling of non-thermal emissions in galaxy clusters, improving the fit to observed radio surface brightness profiles.

Findings

Including sub-halos increases radio emission by 5-20%.

Models with specific neutralino masses fit the radio spectrum without exceeding gamma-ray limits.

The approach reduces the gap in annihilation cross section estimates.

Abstract

Annihilation of Dark Matter (DM) particles has been recognized as one of the possible mechanisms for the production of non-thermal particles and radiation in galaxy clusters. Previous studies have shown that, while DM models can reproduce the spectral properties of the radio halo in the Coma cluster, they fail in reproducing the shape of the radio halo surface brightness because they produce a shape that is too concentrated towards the center of the cluster with respect to the observed one. However, in previous studies the DM distribution was modeled as a single spherically symmetric halo, while the DM distribution in Coma is found to have a complex and elongated shape. In this work we calculate a range of non-thermal emissions in the Coma cluster by using the observed distribution of DM sub-halos. We find that, by including the observed sub-halos in the DM model, we obtain a radio surface brightness with a shape similar to the observed one, and that the sub-halos boost the radio emission by a factor between 5 and 20%, thus allowing to reduce the gap between the annihilation cross section required to reproduce the radio halo flux and the upper limits derived from other observations, and that this gap can be explained by realistic values of the boosting factor due to smaller substructures. Models with neutralino mass of 9 GeV and composition $\tau^+ \tau^-$, and mass of 43 GeV and composition $b \bar b$ can fit the radio halo spectrum using the observed properties of the magnetic field in Coma, and do not predict a gamma-ray emission in excess compared to the recent Fermi-LAT upper limits. These findings make these DM models viable candidate to explain the origin of radio halos in galaxy clusters. [abridged]