A possible mechanism for the mass ratio limitation in early type   galaxies
  There is an interesting correlation between the central objects and their host galaxies in recent high resolution HST photometry of early type galaxies and Near-IR images of nearby quasar hosts. It has been shown that a) the hosts of these very luminous quasars are likely to be early type galaxies and that b) the mass ratio of central black holes (BHs) and their host spheroidal components ($M_{bh}/M_{spheroid}$) is $\sim 0.002$ within a factor of three. Using the hierarchical galaxy evolution scheme for the formation of early-type galaxies, we present here a general viscous accretion disk model to trace the star formation and central engine evolution before and after mergers. In our model, starbursts and AGN coexist; these two activities compete for the gas supply, interact with each other, probably feed back on each other and lock into a final status. They thus constrain the ratio of central black hole mass and its host spheroidal mass to a universal value of order $10^{-3}$. 
Yiping Wang(1 and 2), Peter L. Biermann(1) ((1) Max-Planck-Institut   f\"ur Radioastronomie, Germany, (2) Purple Mountain Ob...