Outflow and Dense Gas Emission from Massive Infrared Dark Clouds

• Published in: The Astrophysical journal 2007-10, Vol.668 (1), p.348-358
• Main Authors: Beuther, H, Sridharan, T. K
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/521142

Infrared dark clouds are expected to harbor sources in different, very young evolutionary stages. To better characterize these differences, we observed a sample of 43 massive infrared dark clouds, originally selected as candidate high-mass starless cores, with the IRAM 30 m telescope covering spectral line tracers of low-density gas, high-density gas, molecular outflows/jets and temperature effects. The SiO(2-1) observations reveal detections toward 18 sources. Assuming that SiO is exclusively produced by sputtering from dust grains, this implies that at least in 40% of this sample star formation is ongoing. A broad range of SiO line widths is observed (between 2.2 and 65 km s super(-1)), and we discuss potential origins for this velocity spread. While the low-density tracers super(12)CO(2-1) and super(13)CO(1-0) are detected in several velocity components, the high-density tracer H super(13)CO super(+)(1-0) generally shows only a single velocity component and is hence well suited for kinematic distance estimates of IRDCs. Furthermore, the H super(13)CO super(+) line width is on average 1.5 times larger than that of previously observed NH sub(3)(1, 1). This is indicative of more motion at the denser core centers, due to either turbulence or beginning star formation activity. In addition, we detect CH sub(3)CN toward only six sources, whereas CH sub(3)OH is observed toward approximately 40% of the sample. Estimates of the CH sub(3)CN and CH sub(3)OH abundances are low with average values of 1.2 x 10 super(-10) and 4.3 x 10 super(-10), respectively. These results are consistent with chemical models at the earliest evolutionary stages of high-mass star formation. Furthermore, the CH sub(3)OH abundances compare well to recently reported values for low-mass starless cores.