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.

12 pages, aastex, 1 postscript figure; accepted for publication in ApJ Letters; also available at http://www.physics.mcmaster.ca/Wilson_Preprints/

References in corpus (3)

• Multiple CO Transitions, CI, and HCN from the Cloverleaf Quasar
• Atomic Carbon in M82: Physical conditions derived from simultaneous observations of the [CI] fine structure submillimeter wave transitions
• The Density and Temperature of Molecular Clouds in M33

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