The evolving star formation rate: M_⋆ relation and sSFR since z ≃ 5 from the VUDS spectroscopic survey^⋆

¹ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
e-mail: lidia.tasca@lam.fr
² Geneva Observatory, University of Geneva, Ch. des Maillettes 51, 1290 Versoix, Switzerland
³ Institut de Recherche en Astrophysique et Planétologie – IRAP, CNRS, Université de Toulouse, UPS-OMP, 14 avenue E. Belin, 31400 Toulouse, France
⁴ University of Bologna, Department of Physics and Astronomy (DIFA), V.le Berti Pichat, 6/2, 40127 Bologna, Italy
⁵ Instituto de Fisica y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, 1111 Gran Bretaña, Playa Ancha Valparaíso, Chile
⁶ INAF–IASF Milano, via Bassini 15, 20133 Milano, Italy
⁷ INAF–Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
⁸ University of Bologna, Department of Physics and Astronomy (DIFA), V.le Berti Pichat, 6/2, 40127 Bologna, Italy
⁹ Astronomy Department, University of Massachusetts, Amherst, MA 01003, USA
¹⁰ Department of Astronomy, University of Geneva, Ch. d’Écogia 16, 1290 Versoix, Switzerland
¹¹ INAF–IASF Bologna, via Gobetti 101, 40129 Bologna, Italy
¹² Department of Astronomy, California Institute of Technology, 1200 E. California Blvd., MC 249-17, Pasadena, CA 91125, USA
¹³ Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre et Marie Curie, 98bis boulevard Arago, 75014 Paris, France
¹⁴ Institut de Recherche en Astrophysique et Planétologie – IRAP, CNRS, Université de Toulouse, UPS-OMP, 14 avenue E. Belin, 31400 Toulouse, France
¹⁵ SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, EH9 3HJ, UK
¹⁶ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁷ Centro de Estudios de Física del Cosmos de Aragón, 44001 Teruel, Spain
¹⁸ Max-Planck-Institut für Extraterrestrische Physik, Postfach 1312, 85741 Garching bei München, Germany
¹⁹ Department of Astronomy, California Institute of Technology, 1200 E. California Blvd., MC 249–17, Pasadena, CA 91125, USA
²⁰ Research Center for Space and Cosmic Evolution, Ehime University, Bunkyo-cho 2-5, 790-8577 Matsuyama, Japan

Received: 20 November 2014
Accepted: 20 June 2015

Abstract

We study the evolution of the star formation rate (SFR) – stellar mass (M_⋆) relation and specific star formation rate (sSFR) of star-forming galaxies (SFGs) since a redshift z ≃ 5.5 using 2435 (4531) galaxies with highly reliable spectroscopic redshifts in the VIMOS Ultra-Deep Survey (VUDS). It is the first time that these relations can be followed over such a large redshift range from a single homogeneously selected sample of galaxies with spectroscopic redshifts. The log (SFR) − log (M_⋆) relation for SFGs remains roughly linear all the way up to z = 5, but the SFR steadily increases at fixed mass with increasing redshift. We find that for stellar masses M_⋆ ≥ 3.2 × 10⁹M_⊙ the SFR increases by a factor of ~13 between z = 0.4 and z = 2.3. Weextend this relation up to z = 5, finding an additional increase in SFR by a factor of 1.7 from z = 2.3 to z = 4.8 for masses M_⋆ ≥ 10¹⁰M_⊙. We observe a turn-off in the SFR–M_⋆ relation at the highest mass end up to a redshift z ~ 3.5. We interpret this turn-off as the signature of a strong on-going quenching mechanism and rapid mass growth. The sSFR increases strongly up to z ~ 2, but it grows much less rapidly in 2 <z< 5. We find that the shape of the sSFR evolution is not well reproduced by cold gas accretion-driven models or the latest hydrodynamical models. Below z ~ 2 these models have a flatter evolution (1 + z)^Φ with Φ = 2 − 2.25 compared to the data which evolves more rapidly with Φ = 2.8 ± 0.2. Above z ~ 2, the reverse is happening with the data evolving more slowly with Φ = 1.2 ± 0.1. The observed sSFR evolution over a large redshift range 0 <z< 5 and our finding of a non-linear main sequence at high mass both indicate that the evolution of SFR and M_⋆ is not solely driven by gas accretion. The results presented in this paper emphasize the need to invoke a more complex mix of physical processes including major and minor merging to further understand the co-evolution of the SFR and stellar mass growth.