Clusters of Galaxies at High Energy Gamma-Rays

Abstract

In the course of the last years clusters of galaxies arouse increasing interest as obvious candidates of a further class of extragalactic objects being able to emit high energy gamma radiation. Supported by observations of diffuse radio halos, hard X-ray and EUV excess emission in galaxy clusters the presence of cosmic ray acceleration processes and its confinement on cosmological timescales has been suggested, high energy gamma-ray emission has been predicted. Gamma radiation can be produced during large—scale cosmological structure formation processes. This theoretical reasoning suggests several scenarios to actually detect galaxy clusters at gamma-ray wavelengths: Either resolved as individual sources of point-like or extended gamma-ray emission, by investigating spatial-statistical correlations with unidentified gamma-ray sources or, if unresolved, through their contribution to the extragalactic diffuse gamma-ray background. In the following I review the status quo concerning the proposed relation between galaxy clusters and high energy gamma-ray observations.KeywordsGalaxy ClusterRoyal AstronRadio HaloAbell ClusterEgret SourceThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.