The detection of [C I] in molecular outflows associated with young stellar objects

The first observations of atomic carbon in molecular outflows are presented. Most of the outflow regions show similar [C I] and ¹³CO line profiles suggesting the [C I] emission from outflow sources traces the same volume of gas as the CO emission, as previous studies have suggested for molecular clouds in general. The [C I] and CO column densities for the 11 sources surveyed are computed over wing and line center velocities. If the [C I] column densities derived from line center velocities are probing conditions in the ambient cloud in the vicinity of the infrared source, then a comparison of these values indicates the carbon abundance in the low-velocity component of the outflows is essentially the same as in the ambient cloud; there is no evidence for shock enhancement of [C I] in the swept-up material. A map of the [C I] emission from the central arcminute of the luminous DR 21 outflow is presented. The [C I] emission is detected from the two CO outflow lobes; [C I] emission from the southwest lobe appears as a limb-brightened, conical shell. Outflow parameters derived from [C I] are consistent with those derived from CO, suggesting the [C I] emission arises from ambient cloud material swept-up by the outflow. The presence of carbon in the swept-up component of the outflows indicates that gas phase carbon is present deep within molecular clouds and is not confined solely to surface layers.