Determine whether gas supply builds the neutral reservoir

Determine whether the gas supply through the surrounding 1–2 virial-radius shell builds the halo’s intrinsic neutral-hydrogen reservoir and thereby affects ignition, using a regression analysis that quantifies the link from shell gas supply to reservoir formation.

Background

The paper frames galaxy ignition as a sequence involving large-scale environment, gas supply through the 1–2 virial-radius shell, assembly of a neutral-hydrogen reservoir, and eventual star formation. The analysis confirms that geometric environment predicts aspects of gas supply and that the neutral reservoir is the strongest direct discriminator of ignition.

However, the connection between gas supply and neutral-reservoir formation is not statistically tested in the paper. Establishing this intermediate link would determine whether environmental effects propagate indirectly to ignition by shaping the reservoir, even though shell gas supply is a weak direct predictor of ignition.

References

The HI reservoir is the decisive'' step here (it is what actually predicts ignition). Meanwhile, the dashed bypass -- traversing directly from the shell-gas supply to ignition, markedinsufficient'' -- performs worse as a direct predictor of ignition. This does not rule out an indirect effect through the reservoir: the middle link, from gas supply to reservoir, carries no label, because unlike the other three it is not backed by a regression statistic in this paper. We defer such an investigation to future work.

— Igniting Galaxy Formation in the Postreionization Universe, II: Nature versus Nurture  (2609.30267 - Moreno et al., 24 Sep 2026) in Figure 7 caption and Section 4.1, “The ignition chain: an emerging picture”

By requiring a resolved gas component, our sample already pre-selects for cosmic-web and backsplash stripping survivors. This paper's nature-over-nurture verdict therefore applies to halos that have already retained enough gas to be resolved; it cannot determine whether environment instead governs that earlier retention stage, where its effect may be strongest.

— Igniting Galaxy Formation in the Postreionization Universe, II: Nature versus Nurture  (2609.30267 - Moreno et al., 24 Sep 2026) in Section 4.4, “Comparison with previous work”