Modelling injection and feedback of Cosmic Rays in grid-based
  cosmological simulations: effects on cluster outskirts
  We present a numerical scheme, implemented in the cosmological adaptive mesh
refinement code ENZO, to model the injection of Cosmic Ray (CR) particles at
shocks, their advection and their dynamical feedback on thermal baryonic gas.
We give a description of the algorithms and show their tests against analytical
and idealized one-dimensional problems. Our implementation is able to track the
injection of CR energy, the spatial advection of CR energy and its feedback on
the thermal gas in run-time. This method is applied to study CR acceleration
and evolution in cosmological volumes, with both fixed and variable mesh
resolution. We compare the properties of galaxy clusters with and without CRs,
for a sample of high-resolution clusters with different dynamical states. At
variance with similar simulations based on Smoothed Particles Hydrodynamics, we
report that the inclusion of CR feedback in our method decreases the central
gas density in clusters, thus reducing the X-ray and Sunyaev-Zeldovich effect
from the clusters centre, while enhancing the gas density and its related
observables near the virial radius.
