GMASS ultradeep spectroscopy of galaxies at z  ~  2^{⋆,⋆⋆,⋆⋆⋆}

VII. Sample selection and spectroscopy

¹ Max-Planck-Institut für Extraterrestrial Physik, Gießenbachstrasse, 85748 Garching bei München, Germany
e-mail: kurk@mpe.mpg.de
² Max-Planck-Institut für Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
³ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁴ Università di Bologna, Dipartimento di Astronomia, via Ranzani 1, 40127 Bologna, Italy
⁵ CEA, Laboratoire AIM, Irfu/SAp, 91191 Gif-sur-Yvette, France
⁶ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁷ NOAO – Tucson, 950 North Cherry Avenue, Tucson, AZ 85719, USA
⁸ Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003, USA
⁹ INAF-Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹⁰ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany

Received: 8 August 2011
Accepted: 17 August 2012

Abstract

Context. Ultra-deep imaging of small parts of the sky has revealed many populations of distant galaxies, providing insight into the early stages of galaxy evolution. Spectroscopic follow-up has mostly targeted galaxies with strong emission lines at z > 2 or concentrated on galaxies at z < 1.

Aims. The populations of both quiescent and actively star-forming galaxies at 1 < z < 2 are still under-represented in our general census of galaxies throughout the history of the Universe. In the light of galaxy formation models, however, the evolution of galaxies at these redshifts is of pivotal importance and merits further investigation. In addition, photometry provides only limited clues about the nature and evolutionary status of these galaxies. We therefore designed a spectroscopic observing campaign of a sample of both massive, quiescent and star-forming galaxies at z > 1.4.

Methods. To determine redshifts and physical properties, such as metallicity, dust content, dynamical masses, and star formation history, we performed ultra-deep spectroscopy with the red-sensitive optical spectrograph FORS2 at the Very Large Telescope. We first constructed a sample of objects, within the CDFS/GOODS area, detected at 4.5 μm, to be sensitive to stellar mass rather than star formation intensity. The spectroscopic targets were selected with a photometric redshift constraint (z > 1.4) and magnitude constraints (B_AB < 26, I_AB < 26.5), which should ensure that these are faint, distant, and fairly massive galaxies.

Results. We present the sample selection, survey design, observations, data reduction, and spectroscopic redshifts. Up to 30 h of spectroscopy of 174 spectroscopic targets and 70 additional objects enabled us to determine 210 redshifts, of which 145 are at z > 1.4. The redshift distribution is clearly inhomogeneous with several pronounced redshift peaks. From the redshifts and photometry, we deduce that the BzK selection criteria are efficient (82%) and suffer low contamination (11%). Several papers based on the GMASS survey show its value for studies of galaxy formation and evolution. We publicly release the redshifts and reduced spectra. In combination with existing and on-going additional observations in CDFS/GOODS, this data set provides a legacy for future studies of distant galaxies.