Black holes and galaxy evolution: Does AGN activity follow or prevent star formation?

Recent years have seen remarkable advances in our understanding of how
supermassive black holes form and grow over cosmic time, and how
energy released by active galactic nuclei (AGN) connects the growth of
black holes to their host galaxies and large-scale structures. Still a
basic and essential question has remained largely unanswered: Does the
fueling of AGN activity *follow* along with star formation in
galaxies, or does feedback from AGN *prevent* star formation? I will
argue that both scenarios take place depending on the properties of
the galaxy and its dark matter halo. Specifically, I will review
recent results suggesting that the long-term rate of black hole
accretion is closely tied to the rate of star formation in the host,
so that essentially all star-forming galaxies may be thought of as
hosting an AGN after accounting for rapid stochastic variability. I
will further discuss the strong evidence that in passive galaxies in
massive halos, mechanical feedback from AGN serves to heat gaseous
atmospheres and prevent further star formation. These results suggest
that the connection between black holes and their host galaxies
changes significantly as halos grow and galaxies evolve from
star-forming to passive systems.