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The aim of our analysis is twofold. On the one hand we are interested inaddressing whether a sample of ETGs morphologically selected differs from asample of passive galaxies in terms of galaxy statistics. On the other hand westudy how the relative abundance of galaxies, the number density and thestellar mass density for different morphological types change over the redshiftrange 0.6<z<2.5. From the 1302 galaxies brighter than Ks=22 selected from theGOODS-MUSIC catalogue, we classified the ETGs on the basis of their morphologyand the passive galaxies on the basis of their sSFR. We proved how thedefinition of passive galaxy depends on the IMF adopted in the models and onthe assumed sSFR threshold. We find that ETGs cannot be distinguished from theother morphological classes on the basis of their low sSFR, irrespective of theIMF adopted in the models. Using the sample of 1302 galaxies morphologicallyclassified into spheroidal galaxies (ETGs) and not spheroidal galaxies (LTGs),we find that their fractions are constant over the redshift range 0.6<z<2.5(20-30% ETGs vs 70-80% LTGs). However, at z<1 these fractions change among thepopulation of the most massive (M*>=10^(11) M_sol) galaxies, with the fractionof massive ETGs rising up to 40% and the fraction of massive LTGs decreasingdown to 60%. Moreover, we find that the number density and the stellar massdensity of the whole population of massive galaxies increase almost by a factorof ~10 between 0.6<z<2.5, with a faster increase of these densities for theETGs than for the LTGs. Finally, we find that the number density of thehighest-mass galaxies (M*>3-4x10^(11) M_sol) both ETGs and LTGs do not increasesince z~2.5, contrary to the lower mass galaxies. This suggests that thepopulation of the most massive galaxies formed at z>2.5-3 and that the assemblyof such high-mass galaxies is not effective at lower redshift.

The population of early-type galaxies: how it evolves with time and how it differs from passive and late-type galaxies