Test whether the first star-formation event rearranges central gas

Investigate whether the first star-formation event rearranges the central gas in a halo and thereby produces the larger neutral-gas radial extent observed in recently ignited halos relative to starless controls.

Background

Recently ignited halos contain more neutral hydrogen and distribute it over a larger normalized half-mass radius than matched starless halos. The paper suggests that the first star-formation event may rearrange central gas, with an observed outflowing double-peanut-shaped overdensity being consistent with this interpretation.

This causal explanation remains untested at the population level. A detailed analysis across the halo population is needed to distinguish whether the extended neutral reservoir precedes ignition or is partly generated by the first star-formation event.

References

Motivated by our representative pair (Figures~\ref{fig:rv} and~\ref{fig:himap}), we speculate that the first star-formation event is responsible for rearranging the central gas -- potentially explaining the radial-extent differences between the ignited and starless samples. The outflowing double peanut-shaped overdensity is consistent with this picture. We defer a detailed, population-wide exploration of this mechanism to future work.

— Igniting Galaxy Formation in the Postreionization Universe, II: Nature versus Nurture  (2609.30267 - Moreno et al., 24 Sep 2026) in Section 4.2, “The HI reservoir’s decoupling”