Molecular cloud structure and star formation near HH 216 in M 16

Abstract

We present millimetre, optical, and near-infrared observations of M 16 in the vicinity of the Herbig-Haro object HH 216. The line profiles of the CO (J = 2-1) spectra are broad and consist of both emission originating from four warm molecular cores and a large cloud or cloud system across the whole field. The CS (J = 2-1) and the C18O (J = 2-1) lines are relatively broad compared with those observed in low-mass star formation regions, but not unusually broad for higher-mass star-forming regions. The virial masses found are much larger than the mass estimates based on the assumption of LTE. The optical images suggest that HH 216 is the terminating bow shock of a large Herbig-Haro flow which includes a jet. A possible location for the driving source is suggested, from the presence of a very reddened point source associated with what may be a small reflection nebula at the tip of a dense molecular "trunk". Another reflection nebula associated with the same core is also detected. This demonstrates that star formation is taking place in the trunk.