Evolution of the specific star formation rate function at z< 1.4 Dissecting the mass-SFR plane in COSMOS and GOODS^⋆

¹ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
e-mail: olivier.ilbert@lam.fr
² AIM, Unité Mixte de Recherche CEA CNRS, Université Paris VII, UMR n158, 75014 Paris, France
³ Laboratoire AIM, CEA/DSM/IRFU, CNRS, Université Paris-Diderot, 91190 Gif-sur-Yvette Cedex, France
⁴ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
⁵ Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125, USA
⁶ Institute of Astronomy and Astrophysics, Academia Sinica, PO Box 23-141, 10617 Taipei, Taiwan, ROC
⁷ Research Center for Space and Cosmic Evolution, Ehime University, 2–5 Bunkyo-cho, 790-8577 Matsuyama, Japan
⁸ Physics Department, Graduate School of Science & Engineering, Ehime University, 2–5 Bunkyo-cho, 790-8577 Matsuyama, Japan
⁹ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
¹⁰ Institute for Astronomy, 2680 Woodlawn Dr., University of Hawaii, Honolulu, Hawaii, HI 96822, USA
¹¹ Department of Physics, ETH Zurich, 8093 Zurich, Switzerland
¹² Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre et Marie Curie, 98bis boulevard Arago, 75014 Paris, France
¹³ Centre de Recherche Astrophysique de Lyon, Université Lyon 1, Observatoire de Lyon, 9 Av. Charles Andrée, 69561 Saint-Genis Laval Cedex, France
¹⁴ Dipartimento di Astronomia, Universita di Padova, vicolo dell’Osservatorio 2, 35122 Padua, Italy
¹⁵ Max-Planck-Institut für Extraterrestrische Physik, Postfach 1312, 85741 Garching bei München, Germany
¹⁶ California Institute of Technology, MC 105-24, 1200 East California Boulevard, Pasadena, CA 91125, USA
¹⁷ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
¹⁸ Kavli Institute for the Physics and Mathematics of the Universe, Todai Institutes for Advanced Study, the University of Tokyo, 277-8583 Kashiwa, Japan
¹⁹ University of Zagreb, Physics Department, Bijenička cesta 32, 10002 Zagreb, Croatia

Received: 17 October 2014
Accepted: 2 March 2015

Abstract

The relation between the stellar mass (M⋆) and the star formation rate (SFR) characterizes how the instantaneous star formation is determined by the galaxy past star formation history and by the growth of the dark matter structures. We deconstruct the M⋆-SFR plane by measuring the specific SFR functions in several stellar mass bins from z = 0.2 out to z = 1.4 (specific SFR = SFR/M_⋆, noted sSFR). Our analysis is primary based on a 24 μm selected catalogue combining the COSMOS and GOODS surveys. We estimate the SFR by combining mid- and far-infrared data for 20500 galaxies. The sSFR functions are derived in four stellar mass bins within the range 9.5 < log (M⋆ /M_⊙) < 11.5. First, we demonstrate the importance of taking into account selection effects when studying the M⋆-SFR relation. Secondly, we find a mass-dependent evolution of the median sSFR with redshift varying as sSFR ∝ (1 + z)^b, with b increasing from b = 2.88^±0.12 to b = 3.78^{± 0.60} between M⋆ = 10^9.75 M_⊙ and M⋆ = 10^11.1 M_⊙, respectively. At low masses, this evolution is consistent with the cosmological accretion rate and predictions from semi-analytical models (SAM). This agreement breaks down for more massive galaxies showing the need for a more comprehensive description of the star formation history in massive galaxies. Third, we obtain that the shape of the sSFR function is invariant with time at z< 1.4 but depends on the mass. We observe a broadening of the sSFR function ranging from 0.28 dex at M⋆ = 10^9.75 M_⊙ to 0.46 dex at M⋆ = 10^11.1 M_⊙. Such increase in the intrinsic scatter of the M⋆-SFR relation suggests an increasing diversity ofstar formation histories (SFHs) as the stellar mass increases. Finally, we find a gradual decline of the sSFR with stellar mass as log ₁₀(sSFR) ∝ −0.17M_⋆. We discuss the numerous physical processes, as gas exhaustion in hot gas halos or secular evolution, which can gradually reduce the sSFR and increase the SFH diversity.