VIMOS Ultra-Deep Survey (VUDS): Witnessing the assembly of a massive cluster at z ~ 3.3 ^{⋆,⋆⋆,⋆⋆⋆}

¹ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
e-mail: brian.lemaux@lam.fr
² INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
³ Instituto de Fisica y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Gran Bretaña 1111, Playa Ancha Valparaíso, Chile
⁴ INAF – IASF, via Bassini 15, 20133 Milano, Italy
⁵ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
⁶ University of Bologna, Department of Physics and Astronomy (DIFA), V.le Berti Pichat, 6/2 – 40127 Bologna, Italy
⁷ INAF – IASF Bologna, via Gobetti 101, 40129 Bologna, Italy
⁸ Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre et Marie Curie, 98bis boulevard Arago, 75014 Paris, France
⁹ Institut de Recherche en Astrophysique et Planétologie – IRAP, CNRS, Université de Toulouse, UPS-OMP, 14 avenue E. Belin, 31400 Toulouse, France
¹⁰ Department of Astronomy, University of Geneva, Ch. d’Écogia 16, 1290 Versoix, Switzerland
¹¹ Geneva Observatory, University of Geneva, Ch. des Maillettes 51, 1290 Versoix, Switzerland
¹² Centro de Estudios de Física del Cosmos de Aragón, Teruel, Spain
¹³ Department of Astronomy, California Institute of Technology, 1200 E. California Blvd., MC 249-17, Pasadena, CA 91125, USA
¹⁴ Astronomy Department, University of Massachusetts, Amherst, MA 01003, USA
¹⁵ Max-Planck-Institut für Extraterrestrische Physik, Postfach 1312, 85741 Garching bei München, Germany
¹⁶ Research Center for Space and Cosmic Evolution, Ehime University, Bunkyo-cho 2-5, 790-8577 Matsuyama, Japan
¹⁷ Department of Physics, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, USA
¹⁸ University of Hawai’i, Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
¹⁹ Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506-0055, USA
²⁰ Laboratoire AIM, CEA/DSM/Irfu/SAp, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France

Received: 17 March 2014
Accepted: 29 July 2014

Abstract

Using new spectroscopic observations obtained as part of the VIMOS Ultra-Deep Survey (VUDS), we performed a systematic search for overdense environments in the early universe (z> 2) and report here on the discovery of Cl J0227-0421, a massive protocluster at z = 3.29. This protocluster is characterized by both the large overdensity of spectroscopically confirmed members, δ_gal = 10.5 ± 2.8, and a significant overdensity in photometric redshift members. The halo mass of this protocluster is estimated by a variety of methods to be ~3 × 10¹⁴ℳ_⊙ at z ~ 3.3, which, evolved to z = 0 results in a halo mass rivaling or exceeding that of the Coma cluster. The properties of 19 spectroscopically confirmed member galaxies are compared with a large sample of VUDS/VVDS galaxies in lower density field environments at similar redshifts. We find tentative evidence for an excess of redder, brighter, and more massive galaxies within the confines of the protocluster relative to the field population, which suggests that we may be observing the beginning ofenvironmentally induced quenching. The properties of these galaxies are investigated, including a discussion of the brightest protocluster galaxy, which appears to be undergoing vigorous coeval nuclear and starburst activity. The remaining member galaxies appear to have characteristics that are largely similar to the field population. Though we find weaker evidence of the suppression of the median star formation rates among and differences in the stacked spectra of member galaxies with respect to the field, we defer any conclusions about these trends to future work with the ensemble of protostructures that are found in the full VUDS sample.