Atomic Carbon Emission from Individual Molecular Clouds in M33
Abstract
We present observations of the 492 GHz [CI] emission for four individual
giant molecular clouds in the Local Group galaxy M33 obtained with the James
Clerk Maxwell Telescope. The average [CI] to CO J=1-0 integrated intensity
ratio of 0.10+/-0.03 is similar to what is observed in Galactic molecular
clouds but smaller than what is seen in starburst galaxies. Similarly, the
column density ratio N(C)/N(CO) is similar to that observed in the Orion Bar,
but smaller than values obtained for starburst galaxies. The [CI] line is found
to be a more important coolant than the lowest three rotational transitions of
CO for all the clouds in the sample. The [CI] luminosity does not appear to be
enhanced significantly in two low-metallicity clouds, which may be due to the
unusual ionization environment of the clouds.