Recombination Lines of Embedded Star Clusters

Abstract

Aims. We are trying to probe conditions in the youngest super star clusters, those still embedded in dense obscuring clouds. Methods. The hydrogen recombination lines in the radio and infrared can be observed through the obscuration, as the optical and UV lines cannot, and give us the kinematics of the ionized gas. Results. The line profiles of the clusters resemble superpositions of the lines of many very young ultra-compact or hyper-compact HII regions. This can be explained if each OB star is individually embedded in dense material which it is accreting, even as it ionizes. Conclusions. We speculate on what this implies for the status and evolutionary state of cluster stars.