Three-dimensional spatial distribution of NGC 6822 globular clusters

Clarify whether the strongly bimodal line-of-sight distances measured for the globular clusters of NGC 6822 represent a genuine physical depth or instead arise from systematic uncertainties in the distance determinations.

Background

The globular clusters in NGC 6822 separate into metal-poor and more metal-rich groups with substantially different mean line-of-sight distances. Because the distance to NGC 6822 itself is poorly constrained and the empirical horizontal-branch calibration may have unquantified systematics for some clusters, the physical interpretation of this bimodality is unresolved.

A genuine line-of-sight depth would provide information about the spatial structure and assembly history of NGC 6822, whereas a systematic origin would instead indicate limitations in the adopted distance methodology. The paper therefore identifies further clarification of the clusters’ three-dimensional distribution as necessary.

References

This result is not yet understood, and the poorly-constrained distance to NGC\,6822 means that either group could, in principle, be consistent with the galaxy's distance. We have highlighted possible systematic effects affecting the distance determination for GCs with low metallicities and red HBs; however, we argue that the most likely such effects would only increase the offset between the distance measurements for the metal-rich and metal-poor red-HB GCs. Therefore, we cannot rule out the possibility of a genuine line-of-sight spread in the distances of the NGC\,6822 GCs.

— Characterising the Globular Cluster Systems of Three Local Group Dwarf Galaxies: NGC6822, NGC147 and NGC185  (2608.28434 - McGill et al., 28 Aug 2026) in Section 6.1, subsection “NGC 6822”; Section 7, Conclusions