[NRL2013] 6673 , the SIMBAD biblio

We have compared stacked spectra of galaxies, grouped by environment and stellar mass, among 58 members of the redshift z=1.24 galaxy cluster RDCS J1252.9-2927 (J1252.9) and 134 galaxies in the z=0.84 cluster RX J0152.7-1357 (J0152.7). These two clusters are excellent laboratories to study how galaxies evolve from star-forming to passive at z∼1. We measured spectral indices and star-forming fractions for our density- and mass-based stacked spectra. The star-forming fraction among low-mass galaxies (<7x10¹⁰M_☉) is higher in J1252.9 than in J0152.7, at about 4σ significance. Thus star formation is being quenched between z=1.24 and z=0.84 for a substantial fraction of low-mass galaxies. Star-forming fractions were also found to be higher in J1252.9 in all environments, including the core. Passive galaxies in J1252.9 have systematically lower D_n4000 values than in J0152.7 in all density and mass groups, consistent with passive evolution at modestly super-solar metallicities.