Signatures of the Youngest Starbursts: The Discovery of Ultradense HII Regions

Extract

Globular clusters are ubiquitous in the local universe, and their younger and bluer siblings, “super star clusters” (SSCs), have been observed in a large number of starburst galaxies. Recently a handful of ultra-young SSCs have been found still embedded in their birth material (e.g. Kobulnicky & Johnson 1999 (here after KJ99); Turner et al. 2000; Beck et al. 2000; Tarchi et al. 2000). Because of their similarity (although on a vastly larger scale) to ultracompact HII regions in the Galaxy, KJ99 dub these embedded massive star clusters “ultradense HII regions” (UDHIIs). I will review the discovery of UDHIIs, their modeled properties, and their connection to the more familiar Galactic ultracompact HII regions.