VVV CL001: Likely the Most Metal-poor Surviving Globular Cluster in the Inner Galaxy

We present the first high-resolution abundance analysis of the globular cluster VVV CL001, which resides in a region dominated by high interstellar reddening toward the Galactic bulge. Using H-band spectra acquired by the Apache Point Observatory Galactic Evolution Experiment, we identified two potential members of the cluster, and estimated from their Fe I lines that the cluster has an average metallicity of [Fe/H] = -2.45 with an uncertainty due to systematics of 0.24 dex. We find that the light-(N), alpha-(O, Mg, Si), and Odd-Z (Al) elemental abundances of the stars in VVV CL001 follo w the same trend as other Galactic metal-poor globular clusters. This makes VVV CL001 possibly the most metalpoor globular cluster identified so far within the Sun's galactocentric distance and likely one of the most metaldeficient clusters in the Galaxy after ESO280-SC06. Applying statistical isochrone fitting, we derive self-consistent age, distance, and reddening values, yielding an estimated age of 11.9(-4.05)(+3.12) Gyr at a distance of 8.22(-1.93)(+1.84) kpc, revealing that VVV CL001 is also an old GC in the inner Galaxy. The Galactic orbit of VVV CL001 indicates that this cluster lies on a halo-like orbit that appears to be highly eccentric. Both chemistry and dynamics support the hypothesis that VVV CL001 could be an ancient fossil relic left behind by a massive merger event during the early evolution of the Galaxy, likely associated with either the Sequoia or the Gaia-Enceladus-Sausage structures.

Automated summary

The study provides the first high-resolution abundance analysis of the globular cluster VVV CL001, suggesting that it may be one of the most metal-deficient clusters in the Galaxy. By applying statistical isochrone fitting, the estimated age of VVV CL001 is around 11.9 Gyr with a distance of approximately 8.22 kpc, indicating that it is an ancient globular cluster in the inner Galaxy. The chemical composition and dynamics support the hypothesis that VVV CL001 could be an ancient fossil relic left behind by a massive merger event during the early evolution of the Galaxy.