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AGN Feedback in Galaxy Formation: Suppressing cluster cooling flows by multiple AGN activity

We apply a spherically symmetric one-dimensional hydrodynamical code to study the heating of the inter-cluster medium (ICM) by AGN activity in cluster galaxies. The AGNs drive bubbles into the ICM and the resulting heating is assumed to be selfregulating. Bubbles affect the ICM in three distinct ways. Firstly, immediately after injection, bubbles expand in situ until they reach pressure equilibrium with the ICM. During this expansion, they heat the ICM by means of weak shocks. Secondly, buoyancy is resisted by viscous or turbulent drag which can also heat the ICM. Thirdly and less importantly, as the bubbles rise by buoyancy, they expand and do adiabatic work which shortens the cooling time in the ICM. The resulting feedback adds considerably to previous estimates of mechanical energy input based only on the observed thermal energy content of x-ray cavities, and suffices to suppress cluster cooling flows. Our self-regulating scenario predicts that there should be enhanced AGN activity of galaxies inside cooling regions compared to galaxies in the outer parts of the cluster. This prediction remains to be confirmed or refuted by observations.