MOLECULAR AND ATOMIC GAS IN THE LARGE MAGELLANIC CLOUD. I. CONDITIONS FOR CO DETECTION

Journal Article · Fri May 01 04:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/696/1/370; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21296221

Wong, T; Welty, D E ^[1]; Hughes, A; Muller, E ^[2]; Fukui, Y; Kawamura, A; Mizuno, N; Mizuno, Y; Murai, M; Onishi, T ^[3]; Ott, J ^[4]; Pineda, J L ^[5]

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1. Astronomy Department, University of Illinois, 1002 W. Green St, Urbana, IL 61801 (United States)
2. CSIRO Australia Telescope National Facility, P.O. Box 76, Epping, NSW 1710 (Australia)
3. Department of Physics, Nagoya University, Chikusa-ku, Nagoya 464-8602 (Japan)
4. National Radio Astronomy Observatory, 520 Edgemont Rd, Charlottesville, VA 22903 (United States)
5. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)

We analyze the conditions for detection of CO(1-0) emission in the Large Magellanic Cloud, using the recently completed second NANTEN CO survey. In particular, we investigate correlations between CO integrated intensity and H I integrated intensity, peak brightness temperature, and line width at a resolution of 2.'6 ({approx}40 pc). We find that significant H I column density (exceeding {approx}10{sup 21} cm{sup -2}) and peak brightness temperature (exceeding {approx}20 K) are necessary but not sufficient conditions for CO detection, with many regions of strong H I emission not associated with molecular clouds. The large scatter in CO intensities for a given H I intensity persists even when averaging on scales of >200 pc, indicating that the scatter is not solely due to local conversion of H I into H{sub 2} near GMCs. We focus on two possibilities to account for this scatter: either there exist spatial variations in the I(CO) to N(H{sub 2}) conversion factor, or a significant fraction of the atomic gas is not involved in molecular cloud formation. A weak tendency for CO emission to be suppressed for large H I linewidths supports the second hypothesis, insofar as large linewidths may be indicative of warm H I, and calls into question the likelihood of forming molecular clouds from colliding H I flows. We also find that the ratio of molecular to atomic gas shows no significant correlation (or anticorrelation) with the stellar surface density, though a correlation with midplane hydrostatic pressure P{sub h} is found when the data are binned in P{sub h} . The latter correlation largely reflects the increasing likelihood of CO detection at high H I column density.

• OSTI ID: 21296221
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 696; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

99 GENERAL AND MISCELLANEOUS
BRIGHTNESS
CORRELATIONS
HYDROGEN
LINE WIDTHS
MAGELLANIC CLOUDS