Past interaction between NGC 6822 and the Milky Way

Determine whether NGC 6822 experienced a past interaction with the Milky Way, including whether it passed within the Milky Way’s virial radius approximately 3–4 Gyr ago.

Background

NGC 6822 is an isolated dwarf irregular galaxy whose complex inner structure has been interpreted as potentially indicating a recent merger or accretion event. The galaxy may also have interacted weakly with the Milky Way several billion years ago, but existing dynamical arguments place a low probability on such an encounter.

Resolving whether this interaction occurred is relevant to interpreting NGC 6822’s structure, stellar populations, and globular-cluster system, particularly because the galaxy lacks clear tidal streams or other obvious signs of a recent interaction.

References

It is suspected that NGC\,6822 may have experienced a weak interaction with the MW, passing within its virial radius $\sim3-4$~Gyrs ago \citep{Zhang2021,Battaglia2022}. However, this is remains uncertain, and \citet{McConnachie2021} argue that the likelihood of a past interaction with the MW is less than 10 per cent.

— 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 2.1, subsection “NGC 6822”