Granato et al (2004) have elaborated a physically grounded model exploiting
the mutual feedback between star-forming spheroidal galaxies and the active
nuclei growing in their cores to overcome, in the framework of the hierarchical
clustering scenario for galaxy formation, one of the main challenges facing
such scenario, the fact that massive spheroidal galaxies appear to have formed
much earlier and faster than predicted by previous semi-analytical models.
After having assessed the values of the two parameters that control the effect
of the complex radiative transfer processes on the time-dependent SEDs we have
compared the model predictions with a variety of IR to mm data. Our results
support a rather strict continuity between objects where stars formed and
evolved massive early-type galaxies, indicating that large spheroidal galaxies
formed most of their stars when they were already assembled as single objects.
The model is successful in reproducing the observed z distribution of K\le20
galaxies at z>1, in contrast with both the classical monolithic and the
semi-analytic models, the ratio of star-forming to passively evolving spheroids
and the counts and z distributions of EROs. The model also favourably compares with the ISOCAM 6.7 mu counts, with the corresponding z distribution, and with IRAC counts, which probe primarily the passive evolution phase, and with the submm SCUBA and MAMBO data, probing the active star-formation phase. The observed fraction of 24mu selected sources with no detectable emission in either the 8mu or R band nicely corresponds to the predicted surface density of star-forming spheroids with 8mu fluxes below the detection limit. Predictions for the z distributions of 24mu sources detected by MIPS surveys are pointed out.
