Lurking systematics in predicting galaxy cold gas masses using dust luminosities and star formation rates

TL;DR

This study evaluates the accuracy of dust luminosity and star formation rate-based methods for predicting galaxy cold gas masses, highlighting systematic biases and limitations, especially at high redshift.

Contribution

It provides calibrated, self-consistent methods for estimating cold gas masses with ~20% accuracy and discusses systematic residuals affecting predictions.

Findings

Dust-based estimates best predict total cold gas mass.

Depletion time methods accurately predict molecular gas mass.

Systematic residuals depend on gas phase partition and can cause up to 0.3dex errors.

Abstract

We use galaxies from the Herschel Reference Survey to evaluate commonly used indirect predictors of cold gas masses. We calibrate predictions for cold neutral atomic and molecular gas using infrared dust emission and gas depletion time methods which are self-consistent and have ~20% accuracy (with the highest accuracy in the prediction of total cold gas mass). However, modest systematic residual dependences are found in all calibrations which depend on the partition between molecular and atomic gas, and can over/under-predict gas masses by up to 0.3dex. As expected, dust-based estimates are best at predicting the total gas mass while depletion time-based estimates are only able to predict the (star-forming) molecular gas mass. Additionally, we advise caution when applying these predictions to high-z galaxies, as significant (0.5dex or more) errors can arise when incorrect assumptions are made about the dominant gas phase. Any scaling relations derived using predicted gas masses may be more closely related to the calibrations used than to the actual galaxies observed.