Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies
  We review the observed demographics and inferred evolution of supermassive
black holes (BHs) found by dynamical modeling of spatially resolved kinematics.
Most influential was the discovery of a tight correlation between BH mass and
the velocity dispersion of the host-galaxy bulge. It and other correlations led
to the belief that BHs and bulges coevolve by regulating each other's growth.
New results are now replacing this simple story with a richer and more
plausible picture in which BHs correlate differently with different galaxy
components. BHs are found in pure-disk galaxies, so classical
(elliptical-galaxy-like) bulges are not necessary to grow BHs. But BHs do not
correlate with galaxy disks. And any correlations with disk-grown pseudobulges
or halo dark matter are so weak as to imply no close coevolution. We suggest
that there are four regimes of BH feedback. 1- Local, stochastic feeding of
small BHs in mainly bulgeless galaxies involves too little energy to result in
coevolution. 2- Global feeding in major, wet galaxy mergers grows giant BHs in
short, quasar-like "AGN" events whose feedback does affect galaxies. This makes
classical bulges and coreless-rotating ellipticals. 3- At the highest BH
masses, maintenance-mode feedback into X-ray gas has the negative effect of
helping to keep baryons locked up in hot gas. This happens in giant,
core-nonrotating ellipticals. They inherit coevolution magic from smaller
progenitors. 4- Independent of any feedback physics, the averaging that results
from successive mergers helps to engineer tight BH correlations.
