Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20921702m&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #217.02; Bulletin of the American Astronomical Society,
Astronomy and Astrophysics
Astronomy
Scientific paper
Very little is known about giant molecular cloud scale variations in the physical conditions of the dense gas component in external galaxies. To understand the physical conditions of the dense component of the ISM in star forming galaxies, we have observed the J = 5 4 transition of HC3N at 2" resolution in the nearby starburst spiral, IC 342, and the dwarf, strong starburst, M 82, with the Very Large Array. These are the first detections of this transition in an external galaxy. The lower energy state of this transition makes it optimal for mapping the relatively quiescent, dense gas. The dataset is used to locate the sites of densest gas, and determine the fraction of the GMCs that have densities >105 cm-3. The HC3N(5-4) emission traces the dense cores seen in HCN, but is much weaker towards the starburst cores. The HC3N(5-4) intensities are compared with existing high resolution, Owen Valley Millimeter Interferometer observations of HC3N(10-9) and an LVG model to determine gas excitation. Densities of the cores are found to be nH2 104.5 cm-3. The excitation temperatures derived from HC3N match well those from 13CO and C18O, indicating that the dense cores associated with the starburst do not have significantly different temperatures than the ambient material they are embedded in. Implications for the efficiency of star formation will be discussed.
Support for this research is provided by NRAO, which is operated by Associated Universities Inc., under cooperative agreement with the National Science Foundation, and by NSF Grants AST-0506669 and AST-0506469.
Meier David Stuart
Turner Jean L.
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