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

TL;DR

This study presents the first high-resolution chemical analysis of the globular cluster VVV CL001, suggesting it is the most metal-poor cluster in the inner Galaxy, and explores its age, orbit, and possible origin as a relic of early Galactic mergers.

Contribution

First detailed chemical and dynamical analysis of VVV CL001, identifying it as a potentially the most metal-poor inner Galaxy globular cluster and linking it to early merger events.

Findings

VVV CL001 has an average metallicity of [Fe/H] = -2.45.

The cluster is approximately 12 billion years old.

It follows a halo-like, highly eccentric orbit.

Abstract

We present the first high-resolution abundance analysis of the globular cluster VVV~CL001, which resides in a region dominated by high interstellar reddening towards the Galactic Bulge. Using \textit{H}-band spectra acquired by the Apache Point Observatory Galactic Evolution Experiment (APOGEE), we identified two potential members of the cluster, and estimate 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 follow the same trend as other Galactic metal-poor globular clusters. This makes VVV~CL001 possibly the most metal-poor globular cluster identified so far within the Sun's galactocentric distance and likely one of the most metal-deficient 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 $11.9^{+3.12}_{-4.05}$ Gyr at a distance of $8.22^{+1.84}_{-1.93}$ 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 \textit{Gaia}-Enceladus-Sausage structures.