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arXiv · 1704.00739

Characterizing the transition from diffuse atomic to dense molecular clouds in the Magellanic clouds with [CII], [CI], and CO

Jorge L. Pineda·William D. Langer·Paul F. Goldsmith·Shinji Horiuchi·Thomas B. H. Kuiper·Erik Muller·Annie Hughes·Juergen Ott·Miguel A. Requena-Torres·Thangasamy Velusamy·Tony Wong
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Abstract

We present and analyze deep Herschel/HIFI observations of the [CII] 158um, [CI] 609um, and [CI] 370um lines towards 54 lines-of-sight (LOS) in the Large and Small Magellanic clouds. These observations are used to determine the physical conditions of the line--emitting gas, which we use to study the transition from atomic to molecular gas and from C^+ to C^0 to CO in their low metallicity environments. We trace gas with molecular fractions in the range 0.1 0.45 in both the LMC and SMC. Ionized carbon is the dominant gas-phase form of this element that is associated with molecular gas, with C^0 and CO representing a small fraction, implying that most (89% in the LMC and 77% in the SMC) of the molecular gas in our sample is CO-dark H2. The mean X_CO conversion factors in our LMC and SMC sample are larger than the value typically found in the Milky Way. When applying a correction based on the filling factor of the CO emission, we find that the values of X_CO in the LMC and SMC are closer to that in the Milky Way. The observed [CII] intensity in our sample represents about 1% of the total far-infrared intensity from the LOSs observed in both Magellanic Clouds.

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Jorge L. Pineda, William D. Langer, Paul F. Goldsmith, Shinji Horiuchi, Thomas B. H. Kuiper, Erik Muller, Annie Hughes, Juergen Ott, Miguel A. Requena-Torres, Thangasamy Velusamy, Tony Wong. 2017-04-12. Characterizing the transition from diffuse atomic to dense molecular clouds in the Magellanic clouds with [CII], [CI], and CO. https://doi.org/10.3847/1538-4357%2Faa683a

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