In and out star formation in z 1.5 quiescent galaxies from rest-frame UV spectroscopy and the far-infrared
Cimatti, A.; Daddi, E.; Béthermin, M.; Zanella, A.; Valentino, F.; Magdis, G.; Sargent, M.; Mignoli, M.; Gobat, R.; Feruglio, C.; Strazzullo, V.; Garilli, B.; Moresco, M.; Pozzetti, L.; Maraston, C.; Renzini, A.; Carollo, M.; Jin, S.; Onodera, M.; Ma, Z.; Cappellari, M.
South Korea, France, Germany, Italy, China, United Kingdom, Denmark, Greece, Switzerland, United States
Abstract
We present a sample of 34 spectroscopically confirmed BzK-selected 1011M⊙ 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 Δage ≤ 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]3727 Å emission line, with SFROII 3.7-4.5M⊙ 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 2-4M⊙ yr-1). This second, photometric sample also displays significant excess at 1.4 GHz, suggestive of the presence of radio-mode AGN activity.
The stacked VIMOS spectrum of all A+B quality ETGs is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/599/A95