In and out star formation in z~1.5 quiescent galaxies from rest-frame UV
  spectroscopy and the far-infrared
  We present a sample of 34 spectroscopically confirmed BzK-selected ~1e11 Msun
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 <1 Gyr 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 ~<0.4 Gyr over ~6 kpc 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]3727A emission line, with
SFR_OII = 3.7-4.5 Msun/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 = 2-4 Msun/yr). This
second, photometric sample also displays significant excess at 1.4 GHz,
suggestive of the presence of radio-mode AGN activity.
