Volume 599, March 2017
|Number of page(s)||12|
|Published online||06 March 2017|
In and out star formation in z ~ 1.5 quiescent galaxies from rest-frame UV spectroscopy and the far-infrared⋆
1 School of Physics, Korea Institute for Advanced Study, Hoegiro 85, Dongdaemun-gu, 02455 Seoul, Republic of Korea
2 Laboratoire AIM-Paris-Saclay, CEA/DSM-CNRS–Université Paris Diderot, Irfu/Service d’Astrophysique, CEA Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette, France
3 Department of Physics, Ludwig-Maximilians-Universität, Scheinerstr. 1, 81679 München, Germany
4 INAF–IASF, via Bassini 15, 20133 Milano, Italy
5 INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
6 Department of Astronomy, University of Science and Technology of China, Hefei, 230026, PR China
7 Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, School of Astronomy and Space Science, Nanjing University, 210093 Nanjing, PR China
8 Institute of Cosmology and Gravitation, Dennis Sciama Building, Burnaby Road, Portsmouth PO1 3FX, UK
9 Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Mariesvej 30, 2100 Copenhagen, Denmark
10 Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, 15236 Athens, Greece
11 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
12 Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
13 Institute for Astronomy, ETH Zurich, 8093 Zurich, Switzerland
14 Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, 30127 Bologna, Italy
15 INAF–Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34143 Trieste, Italy
16 Subaru Telescope, National Astronomical Observatory of Japan, National Institutes of Natural Sciences (NINS), 650 North A’ohoku Place, Hilo, HI 96720, USA
17 Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies), 650 North A’ohoku Place, Hilo, HI 96720, USA
18 INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
19 Astronomy Centre, Department of Physics and Astronomy, University of Sussex, Brighton, BN1 9QH, UK
Received: 5 October 2016
Accepted: 20 December 2016
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.
Key words: galaxies: high-redshift / galaxies: elliptical and lenticular, cD / galaxies: formation / galaxies: stellar content / galaxies: star formation
The stacked VIMOS spectrum of all A+B quality ETGs is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/599/A95
© ESO, 2017
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