Prevalence and physical origin of low-ionization protocluster populations

Determine whether low-ionization galaxy populations are common in overdense environments at redshift greater than six and identify the physical origin of their unusually low ionization states.

Background

The study finds low O32 values in the core of A2744-z7p9OD and notes a similar low-ionization state in the core of the z ≈ 6.9 protocluster SPT0311-58. This possible recurrence suggests that dense protocluster environments may produce ionized-gas conditions different from those in field galaxies.

The available sample is too small to establish whether this is a general property of early protoclusters. The paper also finds that no single examined quantity explains the low O32 values, motivating larger protocluster samples and deeper JWST follow-up to test the prevalence of the population and distinguish among possible physical mechanisms, including multiphase neutral-gas structure.

References

The presence of low O32 values in the cores of both A2744-z7p9OD and SPT0311-58 suggests that dense protocluster environments may host physical conditions with lower gas ionization state, although larger samples of $z>6$ protoclusters are required to determine whether this is a common property.

— RIOJA. Environmental Effects on Stellar Populations and Ionized Gas in a Protocluster at $z=7.88$  (2608.16343 - Osone et al., 17 Aug 2026) in Section 6.2, “The Origin of Low-Ionization Gas in the Protocluster Core”