Origin of extended cool-gas halos around high-redshift galaxies

Determine whether the extended cool-gas halos around high-redshift galaxies originate from star-formation-driven outflows, accreting streams, stripped satellite material, or a combination of these processes.

Background

The paper discusses [C II] 158 μm observations showing that cool gas is more extended than the stellar and dust components of high-redshift star-forming galaxies, sometimes forming halos, plumes, and tidal-like extensions on scales of roughly 10–15 kpc. These structures demonstrate that enriched cool gas was already present around galaxies within the first approximately 0.8–1.5 Gyr of cosmic history.

Several physical mechanisms could produce these extended halos, including winds driven by star formation, inflowing cosmic-gas streams, and material stripped from satellite galaxies. The competing scenarios predict different surface-brightness profiles, kinematics, and metal distributions, motivating sensitive, resolved ALMA2040 observations of individual normal galaxies.

References

These halos show that enriched cool gas is already in place around galaxies within the first $\sim$0.8--1.5\,Gyr, but their origin remains open: star-formation-driven outflows, accreting streams, stripped satellite material, or a combination of these \citep{Pizzati2020,Pizzati2023,liu26}.

— ALMA2040: The High-Redshift Circumgalactic Medium. Imaging the fueling and feedback of galaxies in the early universe  (2610.21776 - Butler et al., 15 Oct 2026) in Section “ALMA2040: Key science cases for the CGM and galactic winds,” subsection “Imaging of the Cool CGM around Normal Star-Forming Galaxies at z ≃ 4–8”