Ubiquity and powering of neutral outflows after quenching

Establish how ubiquitous neutral gas outflows are in galaxies after star formation has ceased and determine whether their properties can be explained by residual star formation alone.

Background

Before this study, neutral-gas kinematics in high-redshift quiescent galaxies were based primarily on a small number of individual objects. The authors therefore identify as unresolved both the prevalence of neutral outflows across the post-star-formation population and the mechanism responsible for powering them.

The paper addresses these questions statistically through Na I D stacking and finds outflows in all quiescent redshift bins, with mass-loading factors and energetics that are difficult to explain using current star formation. Nevertheless, the causal driver remains unresolved because the observations do not uniquely distinguish among AGN activity, fossil feedback, shocks, or other non-stellar processes.

References

Thus, despite emerging evidence for outflows in high-redshift quiescent galaxies, it remains unclear how ubiquitous neutral gas outflows are after star formation has ceased, and whether their properties can be explained by residual star formation alone.

— JWST Spectra Conclusively Show an Excess of Neutral Gas Outflows in Quiescent Galaxies at z=2-5  (2609.09459 - Oh et al., 8 Sep 2026) in Section 1, Introduction

The present data do not permit direct detection of AGN or definitive identification of the origins of the observed outflows, and contributions from shock excitation cannot be excluded.

— JWST Spectra Conclusively Show an Excess of Neutral Gas Outflows in Quiescent Galaxies at z=2-5  (2609.09459 - Oh et al., 8 Sep 2026) in Section 3.2, Non-Stellar Origins of the neutral gas outflows; Section 5, Conclusion

They concluded that it is unclear whether or how these outflows regulate the SF in their host galaxies.

— SQuIGG$\vec{L}$E: Ubiquitous Cool Gas Outflows with Large Mass-Loading Factors in $z\sim0.7$ Post-starburst Galaxies  (2609.31308 - Luo et al., 25 Sep 2026) in Section 5.3, “Outflows in PSBs across Cosmic Time”

It remains possible that L\ PSBs host Na-traced neutral outflows similar to those observed in rapidly quenching galaxies at cosmic noon \citep[e.g.,][]{Davies_2024, Sun_2026}.

— SQuIGG$\vec{L}$E: Ubiquitous Cool Gas Outflows with Large Mass-Loading Factors in $z\sim0.7$ Post-starburst Galaxies  (2609.31308 - Luo et al., 25 Sep 2026) in Appendix, Section “Outflow mass limit”