We present first results of neutral carbon ( [ C I ] ^ { 3 } P _ { 1 } - ^ { 3 } P _ { 0 } at 492 GHz ) and carbon monoxide ( \ce ^13CO , J = 1 - 0 ) mapping in the Vela Molecular Ridge cloud C ( VMR-C ) and 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 \ce ^13CO , with comparable line widths .
We find that [ C I ] has opacity of 0.1 - 1.3 across the mapped region while the [ C I ] / \ce ^13CO peak brightness temperature ratio is between 0.2 to 0.8 .
The [ C I ] column density is an order of magnitude lower than that of \ce ^13CO .
The \ce H2 column density derived from [ C I ] is comparable to values obtained from \ce ^12CO .
Our maps show C I is preferentially detected in gas with low temperatures ( below 20 K ) , which possibly explains the comparable \ce H2 column density calculated from both tracers ( both C I and \ce ^12CO under estimate 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 } - ^ { 3 } P _ { 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 .