VVV CL001: Likely the Most Metal-poor Surviving Globular Cluster in the Inner Galaxy
José G. Fernández-Trincado, Dante Minniti, Stefano O. Souza, Timothy C. Beers, Doug Geisler, Christian Moni Bidin, Sandro Villanova, Steven R. Majewski, Beatriz Barbuy, Angeles Pérez-Villegas, Lady Henao, María Romero-Colmenares, Alexandre Roman-Lopes, Richard R. Lane
Abstract
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 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), α -(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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>11.9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>4.05</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>3.12</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> Gyr at a distance of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>8.22</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.93</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.84</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> 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.