Feedback from a central supermassive black hole is an essential component of galaxy evolution models. Without it, those models cannot produce realistic massive galaxies and galaxy clusters. However, the black-hole feedback mechanism remains mysterious. Somehow, accretion of matter onto the central black hole of a massive galaxy becomes precisely tuned so that it regulates radiative cooling and condensation of gas in a volume many orders of magnitude larger than the black-hole's gravitational zone of influence. I will discuss how the required coupling can arise through condensation and precipitation of cold clouds out of a galaxy's circumgalactic medium, and will show how such a feedback mechanism suspends the circumgalactic medium in a state that is marginally unstable to precipitation. The characteristics of that marginal state turn out to have much in common with observations of the multiphase circumgalactic media around massive galaxies.
Mark Voit (Michigan State University)
Tuesday, 19 September 2017