  Roughly half of all stars reside in galaxies without significant ongoing star
formation. However, galaxy formation models indicate that it is energetically
challenging to suppress the cooling of gas and the formation of stars in
galaxies that lie at the centers of their dark matter halos. In this Letter, we
show that the dependence of quiescence on black hole and stellar mass is a
powerful discriminant between differing models for the mechanisms that suppress
star formation. Using observations of 91 star-forming and quiescent central
galaxies with directly-measured black hole masses, we find that quiescent
galaxies host more massive black holes than star-forming galaxies with similar
stellar masses. This observational result is in qualitative agreement with
models that assume that effective, more-or-less continuous AGN feedback
suppresses star formation, strongly suggesting the importance of the black hole
in producing quiescence in central galaxies.
