results of hydrodynamical simulations of cosmic rays in clusters to our predictions for a dark matter scenario, we find that the ratio of the hard X-ray to gamma-ray emission is a potential diagnostic to understand the origin of non-thermal phenomena in clusters.

In our simulations and analysis, we use the latest LAT instrumental response function and observation strategy and the Fermi Science Tools software package which is currently being used to analyze Fermi data.

As an application of our theoretical study, we present predictions for gamma-ray fluxes from a large X-ray limited sample of 130 nearby groups and clusters of galaxies. Specifically, our predictions are based on X-ray data, and on a fixed set of assumptions for both dark matter and cosmic rays. This also allows for a meaningful comparison of the dark matter to cosmic ray induced emission at gamma-ray frequencies. We present a ranking of plausible candidates where one might expect a bright gamma-ray signal, and of sources where the dark matter contribution is expected to be stronger compared to the one fueled by astrophysical cosmic rays. In particular, we discovered that low-redshift groups are the most promising class of objects to search for a dark matter signal 