Recombination Lines of Embedded Star Clusters

TL;DR

This study uses radio and infrared hydrogen recombination lines to investigate the conditions and kinematics of the youngest embedded super star clusters, revealing complex line profiles indicative of individual star accretion in dense environments.

Contribution

It demonstrates that hydrogen recombination lines can probe the dense, obscured regions of young star clusters and suggests a model of individual star accretion within embedded clusters.

Findings

Line profiles resemble superpositions of ultra-compact HII regions.

Embedded OB stars are likely accreting dense material.

Clusters contain many very young, embedded stars.

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.