The SWIRE-VVDS-CFHTLS surveys: stellar mass assembly over the last 10 Gyr. Evidence for a major build up of the red sequence between z = 2 and z = 1^*

¹ Canada-France-Hawaii Telescope Corporation, Kamuela, HI-96743, USA
² Laboratoire d'Astrophysique de Marseille, UMR 6110, BP 8, 13376 Marseille Cedex 12, France e-mail: arnouts@cfht.hawaii.edu
³ INAF-Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁴ Institute for Astronomy, 2680 Woodlawn Dr., University of Hawaii, Honolulu 96822, Hawaii
⁵ Institut d'Astrophysique de Paris, UMR 7095, 98 bis Bvd Arago, 75014 Paris, France
⁶ Laboratoire d'Astrophysique de Toulouse, UMR 5572, 14 av. E. Belin, 31400 Toulouse, France
⁷ INAF-Osservatorio Astronomico di Brera, via Brera 28, Milan, Italy
⁸ University of California, San Diego 9500 Gilman Dr. La Jolla, CA 92093-0424, USA
⁹ Spitzer Science Center, Mail Stop 314-6, 1200 East California Boulevard, Pasadena, CA 91125, USA
¹⁰ IASF-INAF, via Bassini 15, 20133 Milano, Italy
¹¹ School of Physics & Astronomy, University of Nottingham, University Park, Nottingham, NG72RD, UK
¹² Astrophysical Institute Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
¹³ Centre de Physique Théorique, UMR 6207 CNRS-Université de Provence, 13288 Marseille, France
¹⁴ Geneva Observatory, ch. des Maillettes 51, 1290 Sauverny, Switzerland
¹⁵ INAF-Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy

Received: 12 April 2007
Accepted: 18 September 2007

Abstract

We present an analysis of the stellar mass growth over the last 10 Gyr () using a unique large sample of galaxies selected at m. We have assembled accurate photometric and spectroscopic redshifts for ~21 200 and 1500 galaxies, respectively, with F(3.6 μm) ≥ 9.0 μJy by combining data from Spitzer-SWIRE IRAC, the VIMOS VLT Deep Survey (VVDS), UKIDSS and very deep optical CFHTLS photometry. We split our sample into quiescent (red) and active (blue) galaxies on the basis of an SED fitting procedure that we have compared with the strong rest-frame color bimodality . The present sample contains ~ 4400 quiescent galaxies. Our measurements of the K-rest frame luminosity function and luminosity density evolution support the idea that a large fraction of galaxies is already assembled at z ~ 1.2, with almost 80% and 50% of the active and quiescent populations already in place, respectively. Based on the analysis of the evolution of the stellar mass-to-light ratio (in K-band) for the spectroscopic sub-sample, we derive the stellar mass density for the entire sample. We find that the global evolution of the stellar mass density is well reproduced by the star formation rate derived from UV based measurements when an appropriate dust correction is applied, which supports the idea of an initial mass function that is on average universal. Over the last 8 Gyr (z ≤ 1.2) we observe that the stellar mass density of the active population shows a modest mass growth rate ( ~ 0.005(±0.005) /Mpc³/yr), consistent with a constant stellar mass density, ~ 3.1 10⁸ /Mpc³. In contrast, an increase by a factor of ~2 for the quiescent population over the same timescale is observed. As a consequence, the growth of the stellar mass in the quiescent population must be due to the shutoff of star formation in active galaxies that migrate into the quiescent population. We estimate this stellar mass flux to be ~ 0.017(±0.004) /Mpc³/yr, which balances the major fraction of new stars born according to our best SFR estimate ( = 0.025(±0.003) /Mpc³/yr). From to , we observe a major build-up of the quiescent population with an increase by a factor of ~10 in stellar mass (a mass growth rate of ~ 0.063 /Mpc³/yr). This rapid evolution suggests that we are observing the epoch when, for the first time in the history of the universe, an increasing fraction of galaxies end their star formation activity and start to build up the red sequence.