Searching for Infant Globular Clusters

Kelsey Johnson

The formation of super star clusters represents the most extreme mode of star formation in the local universe. Super star clusters (SSCs) are the most massive and dense type of stellar clusters, and the most massive and dense SSCs are consistent with being the progenitors of the ancient globular clusters which are ubiquitous in the local universe. On the scale of globular cluster lifetimes, SSCs are extremely young objects. However, once these clusters have emerged from their birth material to become visible in optical light, their epoch of formation is past. In recent years, radio observations have revealed a number of massive star clusters which are still deeply embedded in their birth material. These objects appear to be vastly scaled up versions of the ultracompact HII regions which surround extremely young individual massive stars in the Milky Way; this similarity has led us to dub these embedded clusters ultradense HII regions (UDHIIs). The discovery of UDHIIs allows us to begin probing the earliest stages of massive star cluster formation for the first time. In this talk, I will overview what we have learned from the currently known sample of UDHIIs and examine their relation to Galactic UCHIIs.