We present results of an attempt to include more detailed gas physics motivated from hydrodynamical simulations within semi-analytic models (SAM) of galaxy formation, focusing on the role that environmental effects play. Main differences to previous SAMs include taking into account ’gravitational ’ heating of the inter-galactic medium (IGM) by the net surplus of gravitational potential energy released from gas that has been stripped from infalling satellites and the inclusion of dynamical friction heating of the IGM by orbiting satellites. Gravitational heating appears to be an efficient heating source able to prevent cooling in environments corresponding to dark matter halos more massive than ∼ 10 13 M⊙. The energy release by gravitational heating can match that by AGN-feedback in massive galaxies and can exceed it in the most massive ones. However, there is a fundamental difference in the way the two processes operate. Gravitational heating becomes important at late times, when the peak activity of AGNs is already over, and it is very mass dependent. This mass dependency and an
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