Cosmic-ray protons accelerated at cosmological shocks and their impact on groups and clusters of galaxies

We investigate the production of cosmic-ray (CR) protons at cosmological sh ocks by performing, for the first time, numerical simulations of large-scal e structure formation that include directly the acceleration, transport, an d energy losses of the high-energy particles. CRs are injected at shocks ac cording to the thermal leakage model and, thereafter, accelerated to a powe r-law distribution as indicated by the test particle limit of the diffusive shock acceleration theory. The evolution of the CR protons accounts for lo sses owing to adiabatic expansion/compression, Coulomb collisions, and inel astic p-p scattering. Our results suggest that CR protons produced at shock s formed in association with the process of large-scale structure formation could amount to a substantial fraction of the total pressure in the intrac luster medium. Their presence should be easily revealed by GLAST (Gamma-Ray Large-Area Space Telescope) through detection of gamma -ray flux from the decay of pi (o) produced in inelastic p-p collisions of such CR protons wit h nuclei of the intracluster gas. This measurement will allow a direct dete rmination of the CR pressure contribution in the intracluster medium. We al so find that the spatial distribution of CR is typically more irregular tha n that of the thermal gas because it is more influenced by the underlying d istribution of shocks. This feature is reflected in the appearance of our g amma -ray synthetic images. Finally, the average CR pressure distribution a ppears statistically slightly more extended than the thermal pressure.