  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 $10^{-3}$.
