Determine the origin of the gas mass and gas fraction–size correlation

Determine which physical process sets the gas mass of star-forming galaxies and explain the origin of the correlation between gas fraction and galaxy size at fixed stellar mass.

Background

The paper contrasts its SFMS-driven explanation of the gas-to-stellar mass relation with gas-centric explanations based on molecular gas scaling relations. The authors argue that gas-centric accounts do not explain what establishes the gas reservoir in the first place or why gas fraction correlates with galaxy size at fixed stellar mass.

Resolving these questions would clarify whether the gas-to-stellar mass relation is fundamental or instead follows from the star-forming main sequence through the identity Mg/M⋆=sSFR/ϵM_{\rm g}/M_\star={\rm sSFR}/\epsilon, with galaxy size tracing the star formation efficiency.

References

This scenario leaves two questions open. First, it does not address which process determines the gas mass in the first place. Second, the gas fraction correlates strongly with galaxy size at fixed stellar mass \citep{zhangEstimatingHIGas2009, catinellaXGASSTotalCold2018}, and for disc galaxies their size is set by the angular momentum acquired from the host halo and the large-scale tidal torque field \citep{efstathiouStabilityMassesDisc1982, moFormationGalacticDiscs1998, shenSizeDistributionGalaxies2003, kravtsovSizeVirialRadiusRelation2013}. A gas-centric account is therefore complete only once it explains what sets the gas mass and where the gas fraction--size correlation comes from.

— 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”