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Description
We present a sample of 34 spectroscopically confirmed BzK-selected ~10^11^M_{sun}_ quiescent galaxies (pBzK) in the COSMOS field. The targets were initially observed with VIMOS on the VLT to facilitate the calibration of the photometric redshifts of massive galaxies at z>~1.5. Here we describe the reduction and analysis of the data, and the spectrophotometric properties of these pBzK galaxies. In particular, using a spatially resolved median 2D spectrum, we find that the fraction of stellar populations with ages <1Gyr is at least 3 times higher in the outer regions of the pBzK galaxies than in their cores. This results in a mild age gradient of {DELTA}age<=0.4Gyr over ~6kpc and suggests either the occurrence of widespread rejuvenation episodes or that inside-out quenching played a role in the passivization of this galaxy population. We also report on low-level star formation rates derived from the [OII]3727{AA} emission line, with SFR_OII_~3.7-4.5M_{sun}_/yr. This estimate is confirmed by an independent measurement on a separate sample of similarly-selected quiescent galaxies in the COSMOS field, using stacked far-infrared data (SFR_FIR_~2-4M_{sun}_/yr). This second, photometric sample also displays significant excess at 1.4GHz, suggestive of the presence of radio-mode AGN activity.
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