Quenching as a Contest between Galaxy Halos and their Central Black
  Holes
  Existing models of galaxy formation have not yet explained striking
correlations between structure and star-formation activity in galaxies, notably
the sloped and moving boundaries that divide star-forming from quenched
galaxies in key structural diagrams. This paper uses these and other relations
to ``reverse-engineer'' the quenching process for central galaxies. The basic
idea is that star-forming galaxies with larger radii (at a given stellar mass)
have lower black-hole masses due to lower central densities. Galaxies cross
into the green valley when the cumulative effective energy radiated by their
black hole equals $\sim4\times$ their halo-gas binding energy. Since
larger-radii galaxies have smaller black holes, one finds they must evolve to
higher stellar masses in order to meet this halo-energy criterion, which
explains the sloping boundaries. A possible cause of radii differences among
star-forming galaxies is halo concentration. The evolutionary tracks of
star-forming galaxies are nearly parallel to the green-valley boundaries, and
it is mainly the sideways motions of these boundaries with cosmic time that
cause galaxies to quench. BH-scaling laws for star-forming, quenched, and
green-valley galaxies are different, and most BH mass growth takes place in the
green valley. Implications include: the radii of star-forming galaxies are an
important second parameter in shaping their black holes; black holes are
connected to their halos but in different ways for star-forming, quenched, and
green-valley galaxies; and the same BH-halo quenching mechanism has been in
place since $z \sim 3$. We conclude with a discussion of black hole-galaxy
co-evolution, the origin and interpretation of BH scaling laws.
