In the local Universe the galaxy population at masses greater than 3x10^10 Msun is dominated by quiescent galaxies. This population has grown in mass and number density since z<1, alongside a signifincat decline in the cosmic star formation rate density. One way to gain insight into the mechanisms leading to star formation quenching and the ensuing build-up of the present-day quiescent massive galaxy population is to trace the evolution with redshift of galaxies stellar populations, such as mean age and metallicity, in relation to galaxy mass and star formation activity.
To this aim we have taken IMACS deep multi-objects rest-frame optical spectroscopy of a sample of 70 galaxies with mass >10^10Msun and redshift z 0.7, including both quiescent and star-forming galaxies. We estimate their stellar ages, metallicities and masses by interpreting stellar absorption features with a bayesian approach, and we compare them with those of low-redshift SDSS galaxies.
I will present the stellar age-mass and stellar metallicity-mass relations at z=0.7 for the population as a whole and for quiescent and star-forming galaxies separately. I will discuss the observed evolution to z=0 in terms of simple evolutionary scenarios such a passive evolution. Such a study paves the way for similar analysis on larger samples and to higher redshifts with NIR multi-object spectrographs on next-generation telescopes.