VVDS-SWIRE^*

Clustering evolution from a spectroscopic sample of galaxies with redshift 0.2 < z < 2.1 selected from Spitzer IRAC 3.6 μm and 4.5 μm photometry

¹ Laboratoire d'Astrophysique de Marseille, UMR 6110 CNRS-Université de Provence, BP 8, 13376 Marseille Cedex 12, France e-mail: sylvain.delatorre@oamp.fr
² INAF-Osservatorio Astronomico di Brera, via Brera 28, Milan, Italy
³ Department of Astronomy, Cornell University, Space Sciences Building, Ithaca, NY 14853, USA
⁴ Infrared Processing & Analysis Center, California Institute of Technology, MS 100-22, Pasadena, CA 91125, USA
⁵ Center for Astrophysics & Space Sciences, University of California San Diego, La Jolla, CA 92093-0424, USA
⁶ IASF-INAF, via Bassini 15, 20133 Milano, Italy
⁷ Astronomy Centre, University of Sussex, Brighton BN1 9QH, UK
⁸ Geneva Observatory, ch. des Maillettes 51, 1290 Sauverny, Switzerland
⁹ Spitzer Science Center, California Institute of Technology, Mail Stop 314-6, 1200 East California Boulevard, Pasadena, CA 91125, USA
¹⁰ Laboratoire d'Astrophysique de l'Observatoire Midi-Pyrénées (UMR 5572), 14 avenue E. Belin, 31400 Toulouse, France
¹¹ IRA-INAF, via Gobetti, 101, 40129 Bologna, Italy
¹² INAF-Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
¹³ INAF-Osservatorio Astronomico di Bologna, via Ranzani, 1, 40127 Bologna, Italy
¹⁴ Max Planck Institut fur Astrophysik, 85741, Garching, Germany
¹⁵ Institut d'Astrophysique de Paris, UMR 7095, 98bis Bvd. Arago, 75014 Paris, France
¹⁶ School of Physics & Astronomy, University of Nottingham, University Park, Nottingham, NG72RD, UK
¹⁷ Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
¹⁸ Institute for Astronomy, 2680 Woodlawn Dr., University of Hawaii, Honolulu, 96822, Hawaii
¹⁹ Università di Bologna, Dipartimento di Astronomia, via Ranzani 1, 40127 Bologna, Italy
²⁰ Observatoire de Paris, LERMA, 61 avenue de l'Observatoire, 75014 Paris, France
²¹ Centre de Physique Théorique, UMR 6207 CNRS-Université de Provence, 13288 Marseille, France
²² Integral Science Data Centre, Ch. d'Écogia 16, 1290 Versoix, Switzerland
²³ INAF-Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
²⁴ Centro de AstrofÃnsica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
²⁵ Universitá di Milano-Bicocca, Dipartimento di Fisica, Piazza delle Scienze 3, 20126 Milano, Italy

Received: 24 January 2007
Accepted: 26 July 2007

Abstract

Aims.By combining data from the VIMOS VLT Deep Survey (VVDS) with the Spitzer Wide-area InfraRed Extragalactic survey (SWIRE), we have built the currently largest spectroscopic sample of high redshift galaxies selected in the rest-frame near-infrared. We have obtained 2040 spectroscopic redshifts of galaxies with < 21.5 at 3.6 μm, and 1255 spectroscopic redshifts of galaxies with < 21. These allow us to investigate the clustering evolution of galaxies selected via their rest-frame near-infrared luminosity in the redshift range 0.2 < z < 2.1.

Methods.We use the projected two-point correlation function to study the three dimensional clustering properties of galaxies detected at 3.6 μm  and 4.5 μm with the InfraRed Array Camera (IRAC) in the SWIRE survey with measured spectroscopic redshifts from the first epoch VVDS. We compare these properties to those of a larger sample of 16672 SWIRE galaxies for which we have accurate photometric redshifts in the same field.

Results.We find that in the 3.6 μm and 4.5 μm flux limited samples, the apparent correlation length does not change from redshift ~2 to the present. The measured correlation lengths have a mean value of r₀ 3.9±0.5 h^-1 Mpc for the galaxies selected at 3.6 μm and a mean value of r₀ 4.4±0.5 h^-1 Mpc for the galaxies selected at 4.5 μm, across the whole redshift range explored. These values are larger than those typicaly found for I-band selected galaxies at I_AB < 24, for which r₀ varies from 2.69 h^-1 Mpc to 3.63 h^-1 Mpc between z = 0.5 to . We find that the difference in correlation length between I-band and 3.6-4.5 μm selected samples decreases with increasing redshift, becoming comparable at z 1.5. We interpret this as evidence that galaxies with older stellar populations and galaxies actively forming stars reside in comparably over-dense environments at epochs earlier than z 1.5, supporting the recently reported flattening of the color-density relation at high redshift. The increasing difference in correlation length with cosmic time observed between rest-frame UV-optical and near-infrared selected samples could then be an indication that star formation is gradually shifting to lower density regions with decreasing redshift, while the older, passively evolving galaxies remain in the most over-dense peaks.