The structure and kinematics of the DR21 region

• Published in: Monthly notices of the Royal Astronomical Society 1986-03, Vol.219 (1), p.167-190
• Main Authors: Richardson, K. J., White, Glenn J., Phillips, J. P., Avery, L. W.
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; H ii regions. Emission and reflection nebulae; Interstellar medium (ism) and nebulae in milky way; Stellar systems. Galactic and extragalactic objects and systems. The universe
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/219.1.167

Observations of the DR21/DR21(OH) region have been made in the molecular lines CO J = 2–1, CO J = 3–2, HCN J = 4–3, HCO+ J = 4–3, H13CO+ J = 4–3 and CS J = 7–6, supplemented by continuum observations of DR21 and DR21(OH) at 350µm and a 20µm map of DR21. The CO observations show a high-velocity wing region around DR21, which is blue shifted with respect to the −3 km s−1 central velocity of the source, has an observed diameter of ∼1 arcmin NS, ∼3–4 arcmin EW, and may be due loan outflow. The 11 km s−1 component associated with W75N is in evidence over much of the region as foreground material of density ∼103 cm−3. The kinematics of the CO-emitting region are discussed; a simple LVG model would appear to be inadequate. DR21 and DR21 (OH) show up as compact (≲ 1 arcmin diameter) regions of high intensity in the submillimetre continuum and the HCN, HCO+ and CS lines, and their masses are deduced to be ⋍5.7×10 and 7.9×103 M⊙ respectively. The central square arcmin of DR21 is discussed in detail. The CS, HCN, HCO+ and H13CO+ intensities, spatial extents and line profiles, in addition to the self-absorptions seen in some CO lines, can be understood on the basis of a simple 2-component model similar to that of Norman & Silk and consisting of dense (105–106 cm−3) clumps surrounded by a less dense (∼103 cm−3) interclump gas of higher temperature. A combined spatial and velocity dilution factor of ∼0.1 is derived for the clumps. The value of XHCO+ is constrained to be between 10−9 and 10−8, the exact value depending on the assumed clump sizes and velocity widths. The high-excitation transitions we have observed are less contaminated by absorption and emission in the interclump medium than the HCN, H2CO and NH3 lines in which the source has previously been observed at higher resolution, and we discuss the feasibility of detecting the clumps directly in these submillimetre transitions.