Astronomy and Astrophysics, volume 382, 624-638 (2002/2-1)
Radio-millimetre investigation of galactic infrared dark clouds.
TEYSSIER D., HENNEBELLE P. and PERAULT M.
Abstract (from CDS):
We present follow-up observations of the mid-Infrared dark clouds selected from the ISOGAL inner Galaxy sample. On-the-fly maps of 13
O and the 1.2mm continuum emission were conducted at the IRAM 30-m telescope, showing spectacular correlation with the mid-IR absorption. The dark clouds are distributed as far as the prominent molecular ring at a distance of 3 to 7kpc from the Sun. The clouds exhibit shapes ranging from globules to thin filaments down to ≲1pc in size. The on-the-fly images obtained in 13
CO and C18
O confirmed that the cores are dense, compact molecular emitters, significantly more massive than local dark clouds (more than 1000M☉
) and lie within low activity Giant Molecular Clouds (GMC's). Ratios of the emission in the J=(2-1) and (1-0) transitions of 13
CO and C18
O show a remarkable uniformity within each cloud, with a significant portion of the sample represented well by a ratio of 0.67±0.12. Preliminary analysis of temperature and density measurements reveals that most of the cores have densities above 105
and temperatures between 8 and 25 K, these latter clouds being associated with young embedded stars. Despite the high extinction inferred from mid-IR (Av
>50, Hennebelle et al., 2001A&A...365..598H
), the molecular lines are surprisingly weak, indicating likely depletion onto cold grains.
ISM: clouds - molecules - structure - radio continuum: ISM - radio lines: ISM
Table 2: [THP2002] DF +LL.ll+B.bb N=13.
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