The VIMOS Ultra-Deep Survey: ~10 000 galaxies with spectroscopic redshifts to study galaxy assembly at early epochs 2 < z ≃ 6 ^⋆,⋆⋆

¹ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
e-mail: olivier.lefevre@lam.fr
² INAF–Osservatorio Astronomico di Bologna, via Ranzani,1, 40127 Bologna, Italy
³ INAF–IASF, via Bassini 15, 20133 Milano, Italy
⁴ INAF–Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
⁵ University of Bologna, Department of Physics and Astronomy (DIFA), V.le Berti Pichat, 6/2 – 40127 Bologna, Italy
⁶ INAF–IASF Bologna, via Gobetti 101, 40129 Bologna, Italy
⁷ Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre et Marie Curie, 98bis boulevard Arago, 75014 Paris, France
⁸ Institut de Recherche en Astrophysique et Planétologie – IRAP, CNRS, Université de Toulouse, UPS-OMP, 14 avenue E. Belin, 31400 Toulouse, France
⁹ Department of Astronomy, University of Geneva, Ch. d’Écogia 16, 1290 Versoix, Switzerland
¹⁰ Geneva Observatory, University of Geneva, Ch. des Maillettes 51, 1290 Versoix, Switzerland
¹¹ Centro de Estudios de Física del Cosmos de Aragón, 44001 Teruel, Spain
¹² Department of Astronomy, California Institute of Technology, 1200 E. California Blvd., MC 249–17, Pasadena, CA 91125, USA
¹³ Astronomy Department, University of Massachusetts, Amherst, MA 01003, USA
¹⁴ Max-Planck-Institut für Extraterrestrische Physik, Postfach 1312, 85741 Garching bei München, Germany
¹⁵ Research Center for Space and Cosmic Evolution, Ehime University, Bunkyo-cho 2-5, 790-8577 Matsuyama, Japan

Received: 18 March 2014
Accepted: 7 January 2015

Abstract

We present the VIMOS Ultra Deep Survey (VUDS), a spectroscopic redshift survey of ~10 000 very faint galaxies to study the main phase of galaxy assembly in 2 < z ≃ 6. The survey covers 1 deg² in three separate fields: COSMOS, ECDFS, and VVDS-02h, with the selection of targets based on an inclusive combination of photometric redshifts and colour properties. Spectra covering 3650 < λ < 9350 Å are obtained with VIMOS on the ESO-VLT with integration times of 14h. Here we present the survey strategy, target selection, data processing, and the redshift measurement process with an emphasis on the specific methods used to adapt to this high-redshift range. We discuss the spectra quality and redshift reliability and derive a success rate in redshift measurement of 91%, or 74% by limiting the dataset to the most reliable measurements, down to a limiting magnitude i_AB = 25. Measurements are performed all the way down to i_AB = 27. The mean redshift of the main sample is z ~ 3 and extends over a broad redshift range mainly in 2 < z < 6. At 3 < z < 5, the galaxies cover a wide range of luminosities −23 < M_NUV < −20.5, stellar mass 10⁹M_⊙ < M_∗ < 10¹¹M_⊙, and star formation rates 1M_⊙/yr < SFR < 10³M_⊙/yr. We discuss the spectral properties of galaxies using individual as well asstacked spectra. The comparison between spectroscopic and photometric redshifts as well as colour selection demonstrate the effectiveness of our selection scheme. From about ~ 90% of the data analysed so far, we expect to assemble >6000 galaxies with reliable spectroscopic redshifts in 2 < z < 6 when complete. This makes the VUDS the largest survey at these redshifts and offers the opportunity for unprecedented studies of the star-forming galaxy population and its distribution in large-scale structures during the main phase of galaxy assembly.