Red giant branch stars as probes of stellar populations. II. Properties of the newly discovered globular cluster GLIMPSE-C01

TL;DR

This study presents the first detailed analysis of the newly discovered globular cluster GLIMPSE-C01, including its metallicity, distance, structure, and implications for the Milky Way's globular cluster population.

Contribution

It provides the first metallicity, distance, and structural parameters for GLIMPSE-C01, and estimates the number of undiscovered globular clusters in the Milky Way.

Findings

Metallicity estimates around [Fe/H]~-1.4 to -1.6.

Distance approximately 3.7 kpc with high extinction.

At least 10±3 globular clusters remain undiscovered in the Milky Way.

Abstract

Deep near infrared photometry of the newly discovered Galactic globular Cluster GLIMPSE-C01 is reported. We derived for the first time the metal abundance of this object from the slope of the RGB: [Fe/H]=-1.61+/-0.14 in the scale of Zinn (as implemented in Harris 1996), [Fe/H]=-1.44+/-0.12 in the scale of Caretta & Gratton (1997), and [Fe/H]=-1.12+/-0.12 in the scale of Ferraro et al. (1999). The tip and the clump of the red giant branch were used to confirm the estimates of Kobulnicky et al. (2005), placing the cluster at D~3.7+/-0.8 kpc, behind A_v~15 mag of visual extinction. The best fit to the radial surface brightness profile with a single-mass King's model (1962) yielded core radius r_c=0.78 arcmin, tidal radius r_t=27 arcmin, and central concentration c=1.54. Finally, we estimate the number of the "missing" globulars in the central region of the Milky Way. Based on the spatial distribution of the known clusters, and assuming radial symmetry around the Galactic center, we conclude that the Milky Way contains at least 10+/-3 undiscovered objects. The distribution of known clusters in the bulge seem to resemble the orientation of the Milky Way bar.