Characterizing the Transition from Diffuse Atomic to Dense Molecular Clouds in the Magellanic Clouds with [C ii], [C i], and CO

Journal Article · Thu Apr 20 04:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA683A· OSTI ID:22872780

Pineda, Jorge L.; Langer, William D.; Goldsmith, Paul F.; Kuiper, Thomas B. H.; Velusamy, Thangasamy ^[1]; Horiuchi, Shinji ^[2]; Muller, Erik ^[3]; Hughes, Annie ^[4]; Ott, Jürgen ^[5]; Requena-Torres, Miguel A. ^[6]; Wong, Tony ^[7]

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1. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099 (United States)
2. CSIRO Astronomy and Space Science/NASA Canberra Deep Space Communication Complex, P.O. Box 1035, Tuggeranong ACT 2901 (Australia)
3. National Astronomical Observatory of Japan, Chile Observatory, Tokyo, Mitaka, 181-8588 (Japan)
4. CNRS, IRAP, 9 Av. Colonel Roche, BP 44346, 31028, Toulouse Cedex 4 (France)
5. National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801 (United States)
6. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
7. Department of Astronomy, University of Illinois, Urbana, IL 61801 (United States)

We present and analyze deep Herschel/HIFI observations of the [C ii] 158 μm, [C i] 609 μm, and [C i] 370 μm lines toward 54 lines of sight in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC). 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{sup +} to C{sup 0} to CO in their low-metallicity environments. We trace gas with molecular fractions in the range 0.10.45 in both the LMC and the SMC. Ionized carbon is the dominant gas-phase form of this element that is associated with molecular gas, with C{sup 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 H{sub 2}. The mean X{sub 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{sub CO} in the LMC and SMC are closer to that in the Milky Way. The observed [C ii] intensity in our sample represents about 1% of the total far-infrared intensity from the lines of sight observed in both Magellanic clouds.

• OSTI ID: 22872780
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 839; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
CARBON
CARBON IONS
CARBON MONOXIDE
COSMIC GASES
DENSITY
EMISSION
HYDROGEN
MAGELLANIC CLOUDS
METALLICITY
MILKY WAY