Tracing H2 column density with atomic carbon (C i) and co isotopologs
Cunningham, M. R.
Jones, P. A.
Bronfman Aguiló, Leonardo
Cortes, P. C.
Artículo de publicación ISI
We present the first results of neutral carbon ([Ci] 3P1–3P0 at 492 GHz) and carbon monoxide (13CO, J = 1–0)
mapping in the Vela Molecular Ridge cloud C (VMR-C) and the G333 giant molecular cloud complexes with the
NANTEN2 and Mopra telescopes. For the four regions mapped in this work, we find that [Ci] has very similar
spectral emission profiles to 13CO, with comparable line widths. We find that [C i] has an opacity of 0.1–1.3 across
the mapped region while the [Ci]/13CO peak brightness temperature ratio is between 0.2 and 0.8. The [C i] column
density is an order of magnitude lower than that of 13CO. The H2 column density derived from [Ci] is comparable
to values obtained from 12CO. Our maps show that Ci is preferentially detected in gas with low temperatures (below
20 K), which possibly explains the comparable H2 column density calculated from both tracers (both Ci and 12CO
underestimate column density), as a significant amount of the C i in the warmer gas is likely in the higher energy
state transition ([C i] 3P2–3P1 at 810 GHz), and thus it is likely that observations of both the above [C i] transitions
are needed in order to recover the total H2 column density.