Combined CO and Dust Scaling Relations of Depletion Time and Molecular Gas Fractions with Cosmic Time, Specific Star-formation Rate, and Stellar Mass
Berta, S.; Magnelli, B.; Lutz, D.; Wuyts, S.; Förster Schreiber, N. M.; Genzel, R.; Tacconi, L. J.; Cooper, M. C.; Bournaud, F.; Juneau, S.; Saintonge, A.; Colina, L.; Weiss, A.; Burkert, A.; Walter, F.; Lilly, S.; Combes, F.; Feruglio, C.; Bouché, N.; García-Burillo, S.; Sternberg, A.; Weiner, B.; Neri, R.; Cox, P.; Renzini, A.; Boone, F.; Contini, T.; Carollo, M.; Freundlich, J.; Bolatto, A.; Boissier, J.; Lippa, M.; Naab, T.; Gracia-Carpio, J.; Kovac, K.; Salome, P.
Germany, United States, United Kingdom, France, Spain, Switzerland, Chile, Italy, Israel
Abstract
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.
Based on observations with the Plateau de Bure millimetre interferometer, operated by the Institute for Radio Astronomy in the Millimetre Range (IRAM), which is funded by a partnership of INSU/CNRS (France), MPG (Germany), and IGN (Spain).