  We summarize our physical model for the early co-evolution of spheroidal
galaxies and of active nuclei at their centers. Our predictions are in
excellent agreement with a number of observables which proved to be extremely
challenging for all the current semi-analytic models, including the sub-mm
counts and the corresponding redshift distributions, and the epoch-dependent
K-band luminosity function of spheroidal galaxies. Also, the black hole mass
function and the relationship between the black hole mass and the velocity
dispersion in the galaxy are nicely reproduced. The mild AGN activity revealed
by X-ray observations of SCUBA sources is in keeping with our scenario, and
testify the build up of SMBH triggered by intense star formation.
