Determine the Dominant Bias in Molecular Gas Depletion-Time Estimates

Determine whether the omission of extended molecular hydrogen or the selection bias toward the most star-forming galaxies produces the larger bias in the estimated molecular gas depletion times of star-forming and quiescent S0 galaxies.

Background

The study estimates molecular gas masses from Pipe3D Balmer-decrement measurements, which are restricted to the regions covered by the MaNGA bundles and are available only for galaxies with suitable emission-line detections. Consequently, extended molecular hydrogen may be missed, making the derived molecular depletion times upper limits.

The same selection preferentially includes the most actively star-forming galaxies, especially among the quiescent S0 population and, to a lesser extent, the star-forming S0 population. This selection effect would bias the estimated depletion times downward. Because the two effects act in opposite directions, the authors leave unresolved which one dominates.

References

We note here that missed (extended) molecular hydrogen makes all of these estimates upper limits of the molecular depletion time, but the bias towards only the most SF in each sample (particularly the qS0s, but also the SFS0s) would skew them to lower limits. We do not have the information needed to determine which bias is larger.

— The Neutral Hydrogen Gas Content of Star-forming and Quiescent S0 Galaxies  (2609.28030 - Lee et al., 23 Sep 2026) in Section 3, subsection “Molecular Gas Depletion Times” (Section 3.3)