Volume 622, February 2019
|Number of page(s)||27|
|Published online||05 February 2019|
PHIBSS2: survey design and z = 0.5 – 0.8 results
Molecular gas reservoirs during the winding-down of star formation
LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, 75014 Paris, France
2 Collège de France, Paris, France
3 Centre for Astrophysics and Planetary Science, Racah Institute of Physics, The Hebrew University, Jerusalem 91904, Israel
4 Max-Planck-Institute für extraterrestrische Physik (MPE), Giessenbachstrasse 1, 85748 Garching, Germany
5 Dept. of Physics, Le Conte Hall, University of California, Berkeley, CA 94720, USA
6 Dept. of Astronomy, Campbell Hall, University of California, Berkeley, CA 94720, USA
7 Observatorio Astronómico Nacional – OAN, Apartado 1143, 28800 Alcalá de Henares, Madrid, Spain
8 IRAM, 300 rue de la Piscine, 38406 St. Martin d’Heres, Grenoble, France
9 Institut de Recherche en Astrophysique et Planétologie – IRAP, CNRS, Université de Toulouse, UPS-OMP, 14 avenue E. Belin, 31400 Toulouse, France
10 Dept. of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
11 Institute for Astronomy, Department of Physics, ETH Zurich, 8093 Zurich, Switzerland
12 CEA, IRFU, SAp, 91191 Gif-sur-Yvette, France
13 Universitätsternwarte der Ludwig-Maximiliansuniversität, Scheinerstrasse 1, 81679 München, Germany
14 Dept. of Physics & Astronomy, Frederick Reines Hall, University of California, Irvine, CA 92697, USA
15 Institut d’Astrophysique de Paris, Sorbonne Université, CNRS, UMR 7095, 98 bis bd Arago, 7014 Paris, France
16 Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
17 Max Planck Institut für Astrophysik, Karl Schwarzshildstrasse 1, 85748 Garching, Germany
18 INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
19 Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
20 School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
21 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
22 Steward Observatory, 933 N. Cherry Ave., University of Arizona, Tucson, AZ 85721-0065, USA
23 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
24 Department of Physics, University of Bath, Claverton Down, Bath BA2 7AY, UK
Accepted: 18 December 2018
Following the success of the Plateau de Bure high-z Blue Sequence Survey (PHIBSS), we present the PHIBSS2 legacy program, a survey of the molecular gas properties of star-forming galaxies on and around the star-formation main sequence (MS) at different redshifts using IRAM’s NOrthern Extended Millimeter Array (NOEMA). This survey significantly extends the existing sample of star-forming galaxies with CO molecular gas measurements, probing the peak epoch of star formation (z = 1 − 1.6) as well as its building-up (z = 2 − 3) and winding-down (z = 0.5 − 0.8) phases. The targets are drawn from the well-studied GOODS, COSMOS, and AEGIS cosmological deep fields and uniformly sample the MS in the stellar mass (M⋆) – star formation rate (SFR) plane with log(M⋆/M⊙) = 10 − 11.8 and SFR = 3.5 − 500 M⊙ yr−1 without morphological selection, thus providing a statistically meaningful census of star-forming galaxies at different epochs. We describe the survey strategy and sample selection before focusing on the results obtained at redshift z = 0.5 − 0.8, where we report 60 CO(2-1) detections out of 61 targets. We determine molecular gas masses between 2 × 109 and 5 × 1010 M⊙ and separately obtain disc sizes and bulge-to-total (B/T) luminosity ratios from HST I-band images. The median molecular gas-to-stellar mass ratio μgas∼ = 0.28 ± 0.04, gas fraction fgas∼ = 0.22 ± 0.02, and depletion time as well as their dependence with stellar mass and offset from the MS follow published scaling relations for a much larger sample of galaxies spanning a significantly wider range of redshifts, the cosmic evolution of the SFR being mainly driven by that of the molecular gas fraction. The galaxy-averaged molecular Kennicutt–Schmidt (KS) relation between molecular gas and SFR surface densities is strikingly linear, pointing towards similar star formation timescales within galaxies at any given epoch. In terms of morphology, the molecular gas content, the SFR, the disc stellar mass, and the disc molecular gas fraction do not seem to correlate with B/T and the stellar surface density, which suggests an ongoing supply of fresh molecular gas to compensate for the build-up of the bulge. Our measurements do not yield any significant variation of the depletion time with B/T and hence no strong evidence for morphological quenching within the scatter of the MS.
Key words: galaxies: evolution / galaxies: high-redshift / galaxies: star formation / galaxies: ISM / ISM: molecules
© ESO 2019
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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