The Structures and Kinematics of Protoclusters

Abstract

Embedded clusters produce the greatest numbers of stars within our Galaxy but the process by which clusters themselves form is not well understood. The structures and kinematics of the very youngest embedded clusters, i.e., “protoclusters” with ages <106 yr, should provide needed insight. To gauge their utility in this regard, we examine recent observations of a nearby protocluster in Ophiuchus. Near-infrared images of the Oph A core reveal numerous young objects but the small sky coverages or low sensitivities to highly-embedded objects attained so far limit their usefulness in revealing cluster structure. Submillimeter continuum images do reveal the most embedded objects but their relatively low resolutions preclude effective comparisons with near-infrared images. Interferometric millimeter observations of N2H+ 1-0 show a strong spatial coincidence with the submillimeter continuum objects, and can be used to trace radial velocities of this population at least. The Oph A filament shows small radial velocity dispersions, e.g., ∼0.2 km s-1, at odds with predictions from some theories of cluster formation. The upcoming C2D and COMPLETE surveys of nearby star-forming molecular clouds will produce the sensitive, wide-field data needed to understand better the cluster formation process.