Abstract
Infrared Dark Clouds (IRDCs) are a valuable sample to study the initial conditions and the very early stages of the evolution of massive stars. Using the KOSMA telescope, we performed simultaneous single point 12CO(2–1) and (3–2) observations toward 117 IRDCs with a detection rate of 74 % for 12CO(2–1) and 58 % for 12CO(3–2). The non-detected sources are found not to represent real dark clouds. The distances of the IRDCs have been calculated using a Bayesian distance estimator indicating that the sources are mainly concentrated in the Outer, Perseus, Local, Sagittarius and Scutum arms. The excitation temperature and the filling factor have been solved simultaneously for the two emission lines. The average excitation temperature is about 10 K. The filling factors are used to correct the integrated intensity ratio of 12CO(3–2) to (2–1) resulting in a typical value of the ratio of \(0.69\pm0.47\) for the majority of sources. A small number of sources exhibit enhanced values for the ratio because of the presence of a nearby HII region. The ratios do not show significant differences for sources with embedded far-infrared sources.
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Notes
Currently operating in Yangbajing, Tibet, China. http://sgst.bao.ac.cn/.
The GILDAS software is developed by the IRAM (Institute de Radioastronomie Millimétrique). http://www.iram.fr/IRAMFR/GILDAS.
Based on observations obtained with the Planck (http://www.esa.int/Planck), an ESA science mission with instruments and contributions directly funded by ESA Member States, NASA, and Canada.
The fits file is ‘COM_CompMap_ThermalDust-commander_2048_R2.00.fits’ downloaded from online website http://pla.esac.esa.int/pla/#maps.
The data are downloaded from Herschel Science Archive, http://www.cosmos.esa.int/web/herschel/science-archive and the OBSIDs are respectively, 1342185641(+1), 1342193534(+1), 1342196917(+1), 1342207028(+1), 1342211307(+1), 1342218644(+1), 1342218646(+1), 1342218694(+1), 1342218692(+1), 1342218995(+1), 1342244166(+1), 1342244168(+1), 1342244170(+1) and 1342247288(+1).
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Acknowledgements
We thank the anonymous referee for valuable comments and suggestions to improve the quality of the manuscript. This work was funded by The National Natural Science foundation of China under grant 11433008 and was partly supported by National Basic Research Program of China (973 program, 2012CB821802) and the National Natural Science foundation of China under grant 11373062, 11303081, and The Program of the Light in China’s Western Region under grant Nos. RCPY201202 and XBBS-2014-24. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This research is based on observations with AKARI, a JAXA project with the participation of ESA.
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Li, D., Esimbek, J., Zhou, J. et al. KOSMA 12CO(2–1) and (3–2) observations toward Infrared Dark Clouds. Astrophys Space Sci 361, 220 (2016). https://doi.org/10.1007/s10509-016-2807-z
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DOI: https://doi.org/10.1007/s10509-016-2807-z