A young globular cluster in the galaxy NGC 6946

Abstract

A globular cluster ∼ 15 Myr old that contains ∼ 5 × 105 M⊙ of stars inside an ∼11 pc radius has been found in the nearby spiral galaxy NGC 6946, surrounded by clouds of dust and smaller young clusters, inside a giant circular bubble 300 pc in radius. At the edge of the bubble is an arc of regularly spaced clusters that could have been triggered during the bubble's formation. The region is at the end of a spiral arm, suggesting an origin in the asymmetric collapse of spiral-arm gas. This globular cluster is one of the nearest examples of a cluster that is similar to the massive old globular clusters m the Milky Way. We consider the energetics of the bubble and possible formation mechanisms for the globular cluster, including the coalescence of smaller clusters.