The Discovery of Young, Luminous, Compact Stellar Clusters in the Starburst Galaxy NGC 253

Abstract

We report the discovery of four young, luminous, compact stellar clusters in the central region of the starburst spiral galaxy NGC 253. One cluster has an intrinsic M_v of about -15 or brighter, an inferred mass in excess of 1.5X10^6 M_☉, assuming a Salpeter IMF from 0.08M_☉ to l00M_☉, and is resolved with a half-light radius of about 2.5 parsec if it has a radial profile similar to a Galactic globular cluster. The others have intrinsic M_v of about -11 or brighter, inferred masses in excess of 5 X 10^4 M_☉, and are similarly compact. These clusters are excellent candidate young globular clusters. The brighter cluster is similar in luminosity, inferred mass, and compactness to the super star clusters found in other sites of ongoing or recent intense star formation. The location of these clusters in the midst of a starburst region suggests that intense star formation may be a key ingredient in their creation. There are hints that these candidate young globular clusters may be forming with a high specific frequency.