GMASS ultradeep spectroscopy of galaxies at z similar to 2 - III. The emergence of the color bimodality at z similar to 2

Aims: The aim of this work is to study the evolution of the rest-frame color distribution of galaxies with the redshift, in particular in the critical interval 1.4<z<3. Methods: We combined ultradeep spectroscopy from the GMASS project (Galaxy Mass Assembly ultradeep Spectroscopic Survey) with GOODS multi-band photometry (from optical to mid-infrared) to study a sample of 1021 galaxies up to m(4.5 μm) = 23. Results: We find that the distribution of galaxies in the (U-B) color vs. stellar mass plane is bimodal up to at least redshift z=2. We define a “mass complete” sample of galaxies residing on the red sequence, selecting objects with log(M/Msun)>10.1, and we study their morphological and spectro-photometric properties. We show that the contribution to this sample of early-type galaxies, defined as galaxies with a spheroidal morphology and no star formation, decreases from 60-70% at z< 0.5 down to ~50% at redshift z=2. At z>2 we still find red galaxies in the mass complete sample, even if the bimodality is not seen any more. About 25% of these red galaxies at z>2 are passively evolving, with the bulk of their stars formed at redshift z>3.