Combined Co and Dust Scaling Relations of Depletion Time and Molecular Gas Fractions With Cosmic Time, Specific Star-Formation Rate, and Stellar Mass

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 time scale (t depl ) and gas to stellar mass ratio (M molgas /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  H 2 mass conversion factor varies little within ±0.6dex of the main sequence (sSFR(ms,z,M * )), and less than 0.3dex 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 molgas /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 redshift range probed a larger sSFR at constant M * is due to a combination of an increasing gas fraction and a decreasing depletion time scale. As a result galaxy integrated samples of the M molgas -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 molgas with an accuracy of ±0.1dex in relative terms, and ±0.2dex including systematic uncertainties.

Taking care of business in a flash : constraining the time-scale for low-mass satellite quenching with ELVIS

“…While studies of nearby star-forming galaxies suggest that the surface density of ongoing star formation is most closely tied to the dense H2 gas (Bigiel et al , 2011Leroy et al 2008), observed molecular depletion timescales are much shorter than the inferred quenching timescales. For relatively massive galaxies (M 10 10 M ), spanning a broad range of redshift, current observations point towards molecular depletion timescales of roughly 1 − 2 Gyr (Bigiel et al 2011;Leroy et al 2013;Saintonge et al 2011;Tacconi et al 2010Tacconi et al , 2013Genzel et al 2010Genzel et al , 2015. Moreover, recent work targeting larger samples of lower-mass galaxies conclude that the molecular depletion timescale decreases with decreasing stellar mass, such that infalling satellites at 10 9 M should, on average, exhaust their molecular reservoirs in less than 1 Gyr (Saintonge et al 2011;Boselli et al 2014).…”

The Alma Spectroscopic Survey in the Hubble Ultra Deep Field: Molecular Gas Reservoirs in High-Redshift Galaxies

“…with redshift (see also Riechers et al 2010;Casey et al 2011;Geach et al 2011;Aravena et al 2012Aravena et al , 2016Magnelli et al 2012;Bothwell et al 2013;Saintonge et al 2013;Tacconi et al 2013;Chapman et al 2015a;Genzel et al 2015). …”

Evidence of ongoing AGN-driven feedback in a quiescent post-starburst E+A galaxy

“…Thus the stellar mass of the progenitor is M * = 10 10.25 M . Using table 4 in Genzel et al (2015), and assuming that the total gas mass is 1.4 times the molecular gas mass, we obtain Mgas ≈ 10 10.43 M . This value is consistent with gas mass observations in ULIRGs with similar properties (e.g., Solomon et al 1997).…”

“…Genzel et al (2015) combine multiple observations of CO emission and Herschel far-IR dust measurements of over 500 star forming galaxies, and derive molecular gas masses using different methods. Their sample spans the redshift range 0-3, stellar masses of M * = 10 10−11.5 M , and the relative specific star formation rate (sSFR; see definition there) of log(sSFR/sSFR(ms, z, M * )) = −1.5 − 2.…”