zCOSMOS - 10k-bright spectroscopic sample. The bimodality in the Galaxy Stellar Mass Function: exploring its evolution with redshift

submitted to Astronomy and AstrophysicsInternational audienceWe present the Galaxy Stellar Mass Function (GSMF) up to z~1 from the zCOSMOS-bright 10k spectroscopic sample. We investigate the total MF and the contribution of ETGs and LTGs, defined by broad-band SED, morphology, spectral properties or star formation activities. We unveil a galaxy bimodality in the global MF, at least up to the z~0.55, better represented by 2 Schechter functions dominated by ETGs and LTGs, respectively. For the global population we confirm that low-mass galaxies number density increases later and faster than for massive galaxies. We find that the MF evolution at intermediate-low Mstar (logM<10.6) is mostly explained by a growth in stellar mass driven by smooth and decreasing SFHs. The low/negligible evolution at higher Mstar sets a limit of 30-15%, decreasing with redshift, to the fraction of major merging. We find that ETGs increase in number density with cosmic time faster for decreasing Mstar, with a median "building redshift" increasing with mass, in contrast with hierarchical model predictions. For LTGs we find that the number density of blue or spiral galaxies remains almost constant with cosmic time from z~1. Instead, the most extreme population of active star forming galaxies is rapidly decreasing in number density. We suggest, firstly, a transformation from blue active spiral galaxies of intermediate mass into blue quiescent and successively (1-2 Gyr after) into red passive types. The complete morphological transformation into red spheroidal galaxies, required longer time-scales or follows after 1-2 Gyr. A continuous replacement of blue galaxies is expected by low-mass active spirals growing in stellar mass. We estimate that on average ~25% of blue galaxies is transforming into red per Gyr for logM