Confirm Gep I membership in Andromeda XXV

Measure the radial velocity of Gep I to definitively confirm its membership in the Andromeda XXV dwarf spheroidal galaxy and distinguish it from a chance-projected M31 halo globular cluster.

Background

The photometric metallicity, reddening, and distance of Gep I closely match those of the surrounding Andromeda XXV stellar population, strongly supporting a physical association. However, the paper states that photometry alone cannot provide definitive membership confirmation. A radial-velocity measurement is therefore required to test whether Gep I shares the systemic motion of Andromeda XXV rather than being an unrelated M31 halo object projected along the same line of sight.

References

On the basis of the results presented in Section~\ref{sec: CMD_analysis}, our analysis strongly supports the physical association of Gep~I with the And~XXV dSph galaxy, although a definitive confirmation of membership will be possible only by measuring the radial velocity of the cluster.

— The solitary star cluster of the Andromeda XXV dwarf spheroidal  (2608.26959 - Crociati et al., 27 Aug 2026) in Section 3.1, “Gep I as the solitary star cluster of And XXV”; Summary and conclusions