Discovery of a New Low-Latitude Milky Way Globular Cluster Using GLIMPSE

Spitzer Space Telescope imaging from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) reveals a previously unidentified low-latitude rich star cluster near l = 31.°3, b = -0.°1. Near-infrared JHK′ photometry from the Wyoming Infrared Observatory indicates an extinction of AV ≃ 15 ± 3 mag for cluster members. Analysis of 13CO features along the same sight line suggests a probable kinematic distance of 3.1–5.2 kpc. The new cluster has an angular diameter of ∼1–2 pc, a total magnitude corrected for extinction of m = 2.1, and a luminosity of MK ≃ -10.3 at 3.1 kpc. In contrast to young massive Galactic clusters with ages less than 100 Myr, the new cluster has no significant radio emission. Comparison with theoretical K-band luminosity functions indicates an age of at least several gigayears and a mass of at least 105 M⊙. Unlike known old open clusters, this new cluster lies in the inner Galaxy at RGC ≃ 6.1 kpc. We designate this object "GLIMPSE-C01" and present evidence that it is a Milky Way globular cluster passing through the Galactic disk. We also identify a region of star formation and fan-shaped outflows from young stellar objects in the same field as the cluster. The cluster's passage through the Galactic molecular layer may have triggered this star formation activity.