Heating of Gas in Galaxy Groups and Clusters

Was the diffuse gas in galaxy groups and clusters heated at high redshift before it entered a massive halo, or was the heating produced inside collapsed objects by SNII accompanying normal star formation? We compare here two radically different models corresponding to the two scenarios described above. Our results indicate that internal heating by SNII works better than the extreme version of external heating that we adopt in reproducing the observed L-T and entropy-T relations.