The Herschel view of the dominant mode of galaxy growth from z = 4 to the present day^⋆,⋆⋆

¹ Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu – CNRS – Université Paris Diderot, CEA-Saclay, pt courrier 131, 91191 Gif-sur-Yvette, France
e-mail: corentin.schreiber@cea.fr
² Institut d’Astrophysique de Paris, UMR 7095, CNRS, UPMC Univ. Paris 06, 98bis boulevard Arago, 75014 Paris, France
³ National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719, USA
⁴ Max-Planck-Institut für Extraterrestrische Physik (MPE), Postfach 1312, 85741 Garching, Germany
⁵ Argelander-Institut für Astronomie, University of Bonn, auf dem Hägel 71, 53121 Bonn, Germany
⁶ School of Astronomy and Space Sciences, Nanjing University, 210093 Nanjing, PR China
⁷ Astronomy Center, Dept. of Physics & Astronomy, University of Sussex, Brighton BN1 9QH, UK
⁸ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁹ University of California Observatories/Lick Observatory, University of California, Santa Cruz, CA 95064, USA
¹⁰ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹¹ Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA
¹² Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
¹³ Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, 15236 Athens, Greece
¹⁴ Institute for Astronomy, University of Hawaii, Honolulu, Hawaii, HI 96822, USA
¹⁵ Canada-France-Hawaii Telescope, Kamuela, Hawaii, HI 96743, USA
¹⁶ George P. and Cynthia W. Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA
¹⁷ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
¹⁸ Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada

Received: 17 September 2014
Accepted: 23 December 2014

Abstract

We present an analysis of the deepest Herschel images in four major extragalactic fields GOODS–North, GOODS–South, UDS, and COSMOS obtained within the GOODS–Herschel and CANDELS–Herschel key programs. The star formation picture provided by a total of 10 497 individual far-infrared detections is supplemented by the stacking analysis of a mass complete sample of 62 361 star-forming galaxies from the Hubble Space Telescope (HST) H band-selected catalogs of the CANDELS survey and from two deep ground-based K_s band-selected catalogs in the GOODS–North and the COSMOS-wide field to obtain one of the most accurate and unbiased understanding to date of the stellar mass growth over the cosmic history. We show, for the first time, that stacking also provides a powerful tool to determine the dispersion of a physical correlation and describe our method called “scatter stacking”, which may be easily generalized to other experiments. The combination of direct UV and far-infrared UV-reprocessed light provides a complete census on the star formation rates (SFRs), allowing us to demonstrate that galaxies at z = 4 to 0 of all stellar masses (M_∗) follow a universal scaling law, the so-called main sequence of star-forming galaxies. We find a universal close-to-linear slope of the log ₁₀(SFR)–log ₁₀(M_∗) relation, with evidence for a flattening of the main sequence at high masses (log ₁₀(M_∗/M_⊙) > 10.5) that becomesless prominent with increasing redshift and almost vanishes by z ≃ 2. This flattening may be due to the parallel stellar growth of quiescent bulges in star-forming galaxies, which mostly happens over the same redshift range. Within the main sequence, we measure a nonvarying SFR dispersion of 0.3 dex: at a fixed redshift and stellar mass, about 68% of star-forming galaxies form stars at a universal rate within a factor 2. The specific SFR (sSFR = SFR/M_∗) of star-forming galaxies is found to continuously increase from z = 0 to 4. Finally we discuss the implications of our findings on the cosmic SFR history and on the origin of present-day stars: more than two-thirds of present-day stars must have formed in a regime dominated by the “main sequence” mode. As a consequence we conclude that, although omnipresent in the distant Universe, galaxy mergers had little impact in shaping the global star formation history over the last 12.5 billion years.