Gamma Rays from Clusters and Groups of Galaxies: Cosmic Rays versus Dark Matter

Understand

Clusters of galaxies have not yet been detected at gamma-ray frequencies; however, the recently launched Fermi Gamma-ray Space Telescope, formerly known as GLAST, could provide the first detections in the near future.

• Clusters are expected to emit gamma rays as a result of (1) a population of high-energy primary and re-accelerated secondary cosmic rays (CR) fueled by structure formation and merger shocks, active galactic nuclei and supernovae, and (2) particle dark matter (DM) annihilation.
• In this paper, we ask the question of whether the Fermi telescope will be able to discriminate between the two emission processes.
• We present data-driven predictions for a large X-ray flux limited sample of galaxy clusters and groups.