| Summary: | We present spectral line images of [CI] 809 GHz, CO J = 1-0 115 GHz and Hi 1.4 GHz line emission, and calculate the corresponding C, CO and H column densities, for a sinuous, quiescent giant molecular cloud about 5 kpc distant along the l = 328 degrees sightline (hereafter G328) in our Galaxy. The [CI] data comes from the High Elevation Antarctic Terahertz telescope, a new facility on the summit of the Antarctic plateau where the precipitable water vapor falls to the lowest values found on the surface of the Earth. The CO and Hi data sets come from the Mopra and Parkes/ATCA telescopes, respectively. We identify a filamentary molecular cloud, similar to 75 x 5 pc long with mass similar to 4 x 10(4) M-circle dot and a narrow velocity emission range of just 4 km s(-1). The morphology and kinematics of this filament are similar in CO, [CI], and Hi, though in the latter appears as self-absorption. We calculate line fluxes and column densities for the three emitting species, which are broadly consistent with a photodissociation region model for a GMC exposed to the average interstellar radiation field. The [C/CO] abundance ratio averaged through the filament is found to be approximately unity. The G328 filament is constrained to be cold (T-Dust < 20 K) by the lack of far-IR emission, to show no clear signs of star formation, and to only be mildly turbulent from the narrow line width. We suggest that it may represent a GMC shortly after formation, or perhaps still in the process of formation.
|
|---|