Combined CO and Dust Scaling Relations of Depletion Time and Molecular Gas Fractions with Cosmic Time, Specific Star-formation Rate, and Stellar Mass

Reinhard Genzel (1) , L. J. Tacconi (1) , Dieter Lutz (1) , Amélie Saintonge (2) , S. Berta (1) , Benjamin Magnelli (3) , Françoise Combes (4, 5) , Santiago García-Burillo (6) , Roberto Neri (7) , Alberto D. Bolatto (8) , Thierry Contini (9) , S. J. Lilly (10) , Jérémie Boissier (7) , Frédéric Boone (9) , N. Bouché (9) , Frédéric Bournaud (11) , Andreas Burkert (1) , Marcella Carollo (10) , L. Colina (12) , Michael C. Cooper (13) , P. Cox (14) , C. Feruglio (7) , Natascha M. Förster Schreiber (1) , Jonathan Freundlich (4, 5) , J. Graciá-Carpio (1) , Stéphanie Juneau (11) , K. Kovac (10) , Magdalena Lippa (1) , Thorsten Naab (15) , Philippe Salomé (4, 5) , Alvio Renzini (16) , Amiel Sternberg (17) , F. Walter (15) , Benjamin Weiner (18) , Achim Weiss (19) , Stijn Wuyts (1)

1 MPE - Max-Planck-Institut für Extraterrestriche Physik
2 UCL - University College of London [London]
3 Rheinische Friedrich-Wilhelms-Universität Bonn
4 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
5 Galaxies et cosmologie
6 Observatorio Astronomico Nacional, Madrid
7 IRAM - Institut de RadioAstronomie Millimétrique
8 Department of Astronomy, University of Maryland
9 IRAP - Institut de recherche en astrophysique et planétologie
10 ETH Zürich - Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich]
11 DAPNIA - Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée
12 DAMIR/CSIC - Department of Molecular and Infrared Astrophysics, Consejo Superior de Investigaciones Científicas
13 Department of Physics and Astronomy, University of California
14 ALMA - Atacama Large Millimeter Array
15 MPA - Max-Planck-Institut für Astrophysik
16 INAF-Osservatorio Astronomico di Padova
17 TAU - Tel Aviv University
18 Steward Observatory, University of Arizona
19 MPIfR - Max-Planck-Institut für Radioastronomie

We combine molecular gas masses inferred from CO emission in 500 star-forming galaxies (SFGs) between z = 0 and 3, from the IRAM-COLDGASS, PHIBSS1/2, and other surveys, with gas masses derived from Herschel far-IR dust measurements in 512 galaxy stacks over the same stellar mass/redshift range. We constrain the scaling relations of molecular gas depletion timescale (t _depl) and gas to stellar mass ratio (M _{mol gas}/M_* ) of SFGs near the star formation "main-sequence" with redshift, specific star-formation rate (sSFR), and stellar mass (M_* ). The CO- and dust-based scaling relations agree remarkably well. This suggests that the CO --> H₂ mass conversion factor varies little within ±0.6 dex of the main sequence (sSFR(ms, z, M _*)), and less than 0.3 dex throughout this redshift range. This study builds on and strengthens the results of earlier work. We find that t _depl scales as (1 z)^-0.3 × (sSFR/sSFR(ms, z, M _*))^-0.5, with little dependence on M _*. The resulting steep redshift dependence of M _{mol gas}/M _* ≈ (1 z)³ mirrors that of the sSFR and probably reflects the gas supply rate. The decreasing gas fractions at high M_* are driven by the flattening of the SFR-M _* relation. Throughout the probed redshift range a combination of an increasing gas fraction and a decreasing depletion timescale causes a larger sSFR at constant M _*. As a result, galaxy integrated samples of the M _{mol gas}-SFR rate relation exhibit a super-linear slope, which increases with the range of sSFR. With these new relations it is now possible to determine M _{mol gas} with an accuracy of ±0.1 dex in relative terms, and ±0.2 dex including systematic uncertainties.

Domaines: Astrophysique [astro-ph]

Reinhard Genzel, L. J. Tacconi, Dieter Lutz, Amélie Saintonge, S. Berta, et al.. Combined CO and Dust Scaling Relations of Depletion Time and Molecular Gas Fractions with Cosmic Time, Specific Star-formation Rate, and Stellar Mass. The Astrophysical Journal, 2015, 800 (1), pp.20. ⟨10.1088/0004-637X/800/1/20⟩. ⟨hal-03732870⟩