A new empirical method to estimate the molecular gas mass in galaxies

Abstract

We find a tight correlation between the dust extinction, traced by the Balmer Decrement (BD$=$H$\alpha$/H$\beta$), the CO(1-0) line luminosity (L${}_{CO}$) and total molecular gas mass (M${}_{H2}$) in a sample of $222$ local star-forming galaxies drawn from the xCOLD GASS survey. As expected, the galaxy disk inclination affects the correlation by inducing a saturation of the Balmer decrement on highly inclined galaxies. Once this effect is taken into account, L${}_{CO}$ and M${}_{H2}$ can be expressed as a function of BD with a scatter of $\sim 0.3$ dex. We do not find any dependence on galaxy size, mass, morphology, star formation activity, and gas metallicity. The correlation disappears if the atomic gas phase is considered. This is likely due to the fact that the region traced by the BD, the stellar disk, is much smaller than the HI disk.

Accepted to MNRAS letter, 6 pages, 5 figures

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• Dirt-cheap Gas Scaling Relations: Using Dust Absorption, Metallicity and Galaxy Size to Predict Gas Masses for Large Samples of Galaxies
• Evidence of extended cold molecular gas and dust halos around $\mathbf{z}\sim 2.3$ Extremely Red Quasars with ALMA
• Cold gas mass measurements for the era of large optical spectroscopic surveys
• Estimating Molecular Gas Content in Galaxies from PAH Emission
• The dust and cold gas content of local star forming galaxies
• The relationship between cluster environment and molecular gas content of star-forming galaxies in the EAGLE simulation
• MASCOT: Molecular gas depletion times and metallicity gradients -- evidence for feedback in quenching active galaxies
• Relating spatially resolved optical attenuation, dust and gas in nearby galaxies