to the amount of gas contained inside $R_{gal}$.

### Star formation rate.

In the dynamical models, the period of intense star formation, during which most of the star mass is built up, is confined within the first 3 to 4 Gyr. In Model A this is followed by a long tail of minimal stellar activity which continues forever. If this activity would be real, we would expect a background of young stars giving rise to a significant emission in the UV-optical region up to the present, which is not compatible with the observed spectra of typical early-type galaxies. As already pointed out by @Merlin06 this minimal stellar activity is an artefact of the poor mass-resolution for the baryonic component, in other words the low number of particles considered in the numerical simulations. To cope with this, we simply set to zero the star formation rate when only one or two star particles are involved. This is equivalent to cut the star formation rate for ages older than about 5 Gyr. The problem does not occur with model B simply because the last computed models is at 6 Gyr.

### Checking dynamical models against chemo-spectro-photometric models.

To this aim we plug 