Cross-calibration of CO- versus dust-based gas masses and assessment of the dynamical mass budget in Herschel-SDSS Stripe82 galaxies

We present a cross-calibration of CO- and dust-based molecular gas masses at z <= 0.2. Our results are based on a survey with the IRAM30-m telescope collecting CO(1-0) measurements of 78 massive (logM(star)/M-circle dot > 10) galaxies with known gas-phase metallicities and with IR photometric coverage from Wide-field Infrared Survey Explorer (WISE; 22 mu m) and Herschel Spectral and Photometric Imaging Receiver (SPIRE; 250, 350, 500 mu m). We find a tight relation (similar to 0.17 dex scatter) between the gas masses inferred from CO and dust continuum emission, with a minor systematic offset of 0.05 dex. The two methods can be brought into agreement by applying a metallicity-dependent adjustment factor similar to 0.13 dex scatter). We illustrate that the observed offset is consistent with a scenario in which dust traces not only molecular gas but also part of the HI reservoir, residing in the H-2-dominated region of the galaxy. Observations of the CO(2-1) to CO(1-0) line ratio for two-thirds of the sample indicate a narrow range in excitation properties, with a median ratio of luminosities < R-21 > similar to 0.64. Finally, we find dynamical mass constraints from spectral line profile fitting to agree well with the anticipated mass budget enclosed within an effective radius, once all mass components (stars, gas, and dark matter) are accounted for.