2015ApJ...800...20G

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 ⟶ H₂mass 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_deplscales as (1 + z)^–0.3x(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.