Using CS (2-1) to Determine the Galactic Distribution Of Infrared Dark Clouds

Details Using CS (2-1) to Determine the Galactic Distribution Of Infrared Dark Clouds Using CS (2-1) to Determine the Galactic Distribution Of Infrared Dark Clouds

Jan 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21541409f&link_type=abstract

American Astronomical Society, AAS Meeting #215, #414.09; Bulletin of the American Astronomical Society, Vol. 42, p.255

Astronomy and Astrophysics

Astronomy

Scientific paper

Infrared Dark Clouds (IRDCs) are cold, dense molecular clouds which host the earliest stages of high-mass star and cluster formation. A disparity was found in the Galactic distribution of IRDCs in the first and fourth Galactic quadrants. Simon et al. (2006) used the Boston University-Five College Radio Astronomy Observatory (BU-FCRAO) Galactic Ring Survey (GRS) to establish kinematic distances to over 300 IRDCs in the first Galactic quadrant using 13CO (J=1-0) observations. We (Jackson et al. 2008) determined kinematic distances to more than 200 fourth quadrant IRDCs using CS (J=2-1) observations from the Australia Telescope National Facility (ATNF) Mopra Telescope. The peaks of the distributions seem to trace a spiral arm in the Milky Way. However, the distribution in the first quadrant showed an enhancement of IRDCs near the Sun, a population completely absent in the fourth quadrant. This population present in the first quadrant could be a real feature, or could be due to the tracer used. Due to its large critical density, CS unambiguously separates the dense IRDCs from more diffuse giant molecular clouds, while 13CO can pick up the more diffuse clouds. We have repeated our CS (J=2-1) observations with the Mopra Telescope for the first Galactic quadrant. We have found that the population of nearby IRDCs previously detected in the first quadrant are not detected in CS. We determined that the 13CO was indeed tracing a population of lower column density molecular clouds close to the Sun that are not detected in CS.

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