Physical origin of the molecular-gas depletion-time turnover

Determine the physical origin of the tentative turnover in the molecular gas depletion time–effective stellar mass surface density relation for galaxies above and below the star-formation main sequence, using larger galaxy samples to robustly constrain this behavior.

Background

The paper compares the molecular gas depletion time, tdepl,molt_{\rm depl,mol}, with the effective stellar mass surface density, Σeff,∗\Sigma_{\rm eff,*}, for cosmic-noon ASPECS galaxies and local xCOLD GASS galaxies. The authors identify a tentative turnover in this relation for galaxies located above and below the star-formation main sequence. They state that the physical mechanism responsible for this feature is unresolved and that larger samples are needed to determine whether the turnover is statistically robust and to explain its origin.

References

In addition, we identify a tentative turnover in the $t_{\rm depl,mol}$--$\Sigma_{\rm eff,*}$ trend for galaxies above and below the star-formation main sequence in both samples. The physical origin of this turnover remains unclear, and larger samples will be required to robustly constrain this behavior.

— Resolved SED Modeling with JWST and ALMA: The Role of Stellar Mass Surface Density in Regulating Star Formation in Cosmic Noon Galaxies  (2609.12059 - Liao et al., 10 Sep 2026) in Section 6.6, “Relations between molecular gas and $\Sigma_{\rm eff,*}$”

The link between galaxy size and star formation efficiency follows from the star formation law, although the direction of causality remains debated.

— Inflow-driven galaxy evolution - II: A hierarchy in the scaling relations of star-forming galaxies  (2610.12394 - Wang et al., 8 Oct 2026) in Section 5.2, “The origin of the gas-to-stellar mass relation”

These galaxies must therefore have a low star formation efficiency for reasons that are still unclear.

— Probing cold gas and dust in quiescent galaxies across cosmic time  (2610.21513 - Zanella et al., 15 Oct 2026) in Section 1.1.1, “Characterizing the molecular gas reservoirs”