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Gobat, R.; Daddi, E.; Strazzullo, V.; Garilli, B.; Mignoli, M.; Ma, Z.; Jin, S.; Maraston, C.; Magdis, G.; Béthermin, M.; Cappellari, M.; Carollo, M.; Cimatti, A.; Feruglio, C.; Moresco, M.; Onodera, M.; Pozzetti, L.; Renzini, A.; Sargent, M.; Valentino, F.; Zanella, A. (2017): In and out star formation in z similar to 1.5 quiescent galaxies from rest-frame UV spectroscopy and the far-infrared. In: Astronomy & Astrophysics, Vol. 599, A95
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Abstract

We present a sample of 34 spectroscopically confirmed BzK-selected similar to 10(11) M-circle dot 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 greater than or similar to 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 Delta age <= 0.4 Gyr over similar to 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] 3727 angstrom emission line, with SFROII similar to 3.7-4.5 M-circle dot yr (1). 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 (SFRFIR similar to 2-4 M-circle dot yr(-1)). This second, photometric sample also displays significant excess at 1.4 GHz, suggestive of the presence of radio-mode AGN activity.