Abstract

We present the first results of neutral carbon ([C I](3) P-1-P-3(0) at 492 GHz) and carbon monoxide ((CO)-C-13, 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 [C I] has very similar spectral emission profiles to (CO)-C-13, with comparable line widths. We find that [C I] has an opacity of 0.1-1.3 across the mapped region while the [C I]/(CO)-C-13 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 (CO)-C-13. The H-2 column density derived from [C I] is comparable to values obtained from (CO)-C-12. Our maps show that C I is preferentially detected in gas with low temperatures (below 20 K), which possibly explains the comparable H-2 column density calculated from both tracers (both C I and (CO)-C-12 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](3) P-2-P-3(1) 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 H-2 column density.