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Combined CO and dust scaling relations of depletion time and molecular gas fractions with cosmic time, specific star-formation rate, and stellar mass

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

© 2015. The American Astronomical Society. All rights reserved. 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 (tdepl) and gas to stellar mass ratio (Mmol 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 tdepl scales as (1 + z)-0.3 × (sSFR/sSFR(ms, z, M∗))-0.5, with little dependence on M∗. The resulting steep redshift dependence of Mmol 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 Mmol 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 Mmol gas with an accuracy of ±0.1 dex in relative terms, and ±0.2 dex including systematic uncertainties.

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