Black holes, cooling flows and galaxy formation

Abstract

Central black holes in galaxies are now well established as a ubiquitous phenomenon, and this fact is important for theories of cosmological structure formation. Merging of galaxy haloes must preserve the proportionality between black hole mass and baryonic mass; the way in which this happens may help solve difficulties with existing models of galaxy formation, which suffer from excessive cooling and thus overproduce stars. Feedback from active nuclei may be the missing piece of the puzzle, regulating galaxy–scale cooling flows. Such a process now seems to be observed in cluster–scale cooling flows, where dissipation of sound waves generated by radio lobes can plausibly balance the energy lost in X–rays, at least in a time–averaged sense.