The Galactic Distribution of Infrared Dark Clouds

Details The Galactic Distribution of Infrared Dark Clouds The Galactic Distribution of Infrared Dark Clouds

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.9209f&link_type=abstract

American Astronomical Society, AAS Meeting #211, #92.09; Bulletin of the American Astronomical Society, Vol. 39, p.888

Astronomy and Astrophysics

Astronomy

Scientific paper

CS (2-1) measurements toward a large sample of fourth Galactic quadrant infrared dark clouds (IRDCs) were made with the ATNF Mopra telescope in order to establish their kinematic distances and Galactic distribution. Due to its large critical density, CS unambiguously separates the dense IRDCs from more diffuse giant molecular clouds. The fourth quadrant IRDCs show a pronounced peak in their radial Galactocentric distribution at R = 6 kpc. When compared with the distribution of first quadrant IRDCs deduced by 13CO (1-0) emission, we find that the first quadrant distribution also shows a peak, but at a Galactocentric radius of R = 5 kpc rather than 6 kpc. This disparity in Galactocentric radius suggests that IRDCs are tracing a spiral arm which lies closer to the sun in the fourth quadrant. Indeed, the deduced IRDC distribution matches the location of the "Scutum-Centaurus" arm in Milky Way models dominated by two spiral arms. Since OB stars form in spiral arms, this association between IRDCs and the Galactic spiral arm strengthens the suggestion that IRDCs spawn the Galaxy's high-mass stars.
The authors gratefully acknowledge funding support through NASA grant NAG5-10808 and NSF grants AST-0098562 and AST-0507657.

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