2009ApJ...696..370W -
Astrophys. J., 696, 370-384 (2009/May-1)
Molecular and atomic gas in the Large Magellanic Cloud. I. Conditions for CO detection.
WONG T., HUGHES A., FUKUI Y., KAWAMURA A., MIZUNO N., OTT J., MULLER E., PINEDA J.L., WELTY D.E., KIM S., MIZUNO Y., MURAI M. and ONISHI T.
Abstract (from CDS):
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 (∼40 pc). We find that significant H I column density (exceeding ∼1021/cm2) and peak brightness temperature (exceeding ∼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 H2 near GMCs. We focus on two possibilities to account for this scatter: either there exist spatial variations in the I(CO) to N(H2) 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 Ph is found when the data are binned in Ph. The latter correlation largely reflects the increasing likelihood of CO detection at high H I column density.
Abstract Copyright:
∼
Journal keyword(s):
galaxies: ISM - ISM: molecules - Magellanic Clouds
Simbad objects:
4
Full paper
View the references in ADS
To bookmark this query, right click on this link: simbad:2009ApJ...696..370W and select 'bookmark this link' or equivalent in the popup menu