In and out star formation in z ~ 1.5 quiescent galaxies from rest-frame UV spectroscopy and the far-infrared

Raphael Gobat, Emanuele Daddi, V. Strazzullo, Bianca Garilli, M. Mignoli, Zhibo Ma, S. Jin, C. Maraston, G. Magdis, M. Béthermin, Michele Cappellari, M. Carollo, Andrea Cimatti, C. Feruglio, Michele Moresco, M. Onodera, L. Pozzetti, Alvio Renzini, M. Sargent, F. ValentinoA. Zanella

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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.
Original languageEnglish
Article numberA95
Number of pages12
JournalAstronomy and Astrophysics
Early online date6 Mar 2017
Publication statusEarly online - 6 Mar 2017


  • galaxies: high-redshift
  • galaxies: elliptical and lenticular, cD
  • galaxies: formation
  • galaxies: stellar content
  • galaxies: star formation


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