Massive Galaxies in COSMOS: Evolution of Black hole versus bulge mass
  but not versus total stellar mass over the last 9 Gyrs?
  We constrain the ratio of black hole (BH) mass to total stellar mass of
type-1 AGN in the COSMOS survey at 1<z<2. For 10 AGN at mean redshift z~1.4
with both HST/ACS and HST/NICMOS imaging data we are able to compute total
stellar mass M_(*,total), based on restframe UV-to-optical host galaxy colors
which constrain mass-to-light ratios. All objects have virial BH mass-estimates
available from the COSMOS Magellan/IMACS and zCOSMOS surveys. We find zero
difference between the M_BH--M_(*,total)-relation at z~1.4 and the
M_BH--M_(*,bulge)-relation in the local Universe.
  Our interpretation is: (a) If our objects were purely bulge-dominated, the
M_BH--M_(*,bulge)-relation has not evolved since z~1.4. However, (b) since we
have evidence for substantial disk components, the bulges of massive galaxies
(logM_(*,total)=11.1+-0.25 or logM_BH~8.3+-0.2) must have grown over the last 9
Gyrs predominantly by redistribution of disk- into bulge-mass. Since all
necessary stellar mass exists in the galaxy at z=1.4, no star-formation or
addition of external stellar material is required, only a redistribution e.g.
induced by minor and major merging or through disk instabilities. Merging, in
addition to redistributing mass in the galaxy, will add both BH and
stellar/bulge mass, but does not change the overall final M_BH/M_(*,bulge)
ratio.
  Since the overall cosmic stellar and BH mass buildup trace each other tightly
over time, our scenario of bulge-formation in massive galaxies is independent
of any strong BH-feedback and means that the mechanism coupling BH and bulge
mass until the present is very indirect.
