Astrophys. J., 686, 384-398 (2008/October-2)
A 12CO, 13CO, and C18O survey of infrared dark clouds.
DU F. and YANG J.
Abstract (from CDS):
Infrared dark clouds (IRDCs) are extinction features against the Galactic infrared background, mainly in the mid-infrared band. Recently they were proposed to be potential sites of massive star formation. In this work we have made a 12CO, 13CO, and C18O (J=1⟶0) survey of 61 IRDCs, 52 of which are in the first Galactic quadrant, selected from a catalog given by Simon and coworkers, while the others are in the outer Galaxy, selected by visually inspecting the MSX images. Detection rates in the three CO lines are 90%, 71%, and 62%, respectively. The distribution of IRDCs in the first Galactic quadrant is consistent with the 5 kpc molecular ring picture, while a slight trace of a spiral pattern is also noticeable, and needs to be further examined. The IRDCs have a typical excitation temperature of 10 K and typical column density of several 1022/cm2. Their typical physical size is estimated to be several parsecs using angular sizes from the Simon catalog. Typical volume density and typical LTE mass are ∼5000/cm3 and ∼5000 M☉, respectively. The IRDCs are in or near virial equilibrium. The properties of IRDCs are similar to those of star-forming molecular clumps, and they seem to be intermediate between giant molecular clouds and Bok globules; thus they may represent early stages of massive star formation.
ISM: Dust, Extinction - Galaxy: Structure - Infrared: ISM - Radio Lines: ISM - Stars: Formation
VizieR on-line data:
<Available at CDS (J/ApJ/686/384): table1.dat table3.dat table4.dat>
Table 1, col(1): [DY2008] NN (Nos 1-61) = Table 1, col(2): [DY2008] GLLL.ll+BB.bb N=61. Table 3: [DY2008] NNa N=39 added.
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