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

R. Genzel, L. J. Tacconi, D. Lutz, A. Saintonge, S. Berta, B. Magnelli, F. Combes, S. García-Burillo, R. Neri, A. Bolatto, T. Contini, S. Lilly, J. Boissier, F. Boone, N. Bouché, F. Bournaud, A. Burkert, M. Carollo, L. Colina, M. C. CooperP. Cox, C. Feruglio, N. M. Förster Schreiber, J. Freundlich, J. Gracia-Carpio, S. Juneau, K. Kovac, M. Lippa, T. Naab, P. Salome, A. Renzini, A. Sternberg, F. Walter, B. Weiner, A. Weiss, S. Wuyts

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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.
Original languageEnglish
Number of pages20
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 10 Feb 2015



  • galaxies: evolution
  • galaxies: high-redshift
  • galaxies: kinematics and dynamics
  • infrared: galaxies

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