Direct and indirect pieces of observational evidence point to a strong connection between high-redshift quasars and their host galaxies .
In the framework of a model where the shining of the quasar is the episode that stops the formation of the galactic spheroid inside a virialized halo , it has been proven possible to explain the submillimetre source counts together with their related statistics and the local luminosity function of spheroidal galaxies .
The time delay between the virialization and the quasar manifestation required to fit the counts is short and incresing with decresing the host galaxy mass .
In this paper we compute the detailed chemical evolution of gas and stars inside virialized haloes in the framework of the same model , taking into account the combined effects of cooling and stellar feedback .
Under the assumption of negligible angular momentum , we are able to reproduce the main observed chemical properties of local ellipticals .
In particular , by using the same duration of the bursts which are required in order to fit the submillimetre source counts , we recover the observed increase of the Mg/Fe ratio with galactic mass .
Since for the most massive objects the assumed duration of the burst is T _ { burst } \la 0.6 Gyr , we end up with a picture for elliptical galaxy formation in which massive spheroids complete their assembly at early times , thus resembling a monolithic collapse , whereas smaller galaxies are allowed for a more prolonged star formation , thus allowing for a more complicated evolutionary history .
In the framework of the adopted scenario , only quasar activity can provide energies large enough to stop the star formation very soon after virialization in the most massive galactic haloes .
The chemical abundance of the gas that we estimate at the end of the burst matches well the metallicity inferred from the quasar spectra .
Therefore , the assumption that quasar activity interrupts the main episode of star formation in elliptical galaxies turns out to be quite reasonable .
In this scenario , we also point out that non-dusty extremely red objects are the best targets for searching for high-redshift Type Ia supernovae .