The cometary HII regions of DR 21: Bow shocks or champagne flows or both?

Abstract

We present deep Very Large Array H66$\alpha$ radio recombination line (RRL) observations of the two cometary HII regions in DR 21. With these sensitive data, we test the "hybrid" bow shock/champagne flow model previously proposed for the DR 21 HII regions. The ionized gas down the tail of the southern HII region is redshifted by up to ~30 km/s with respect to the ambient molecular gas, as expected in the hybrid scenario. The RRL velocity structure, however, reveals the presence of two velocity components in both the northern and southern HII regions. This suggests that the ionized gas is flowing along cone-like shells, swept-up by stellar winds. The observed velocity structure of the well-resolved southern HII region is most consistent with a picture that combines a stellar wind with stellar motion (as in bow shock models) along a density gradient (as in champagne flow models). The direction of the implied density gradient is consistent with that suggested by maps of dust continuum and molecular line emission in the DR 21 region.

22 pages, 9 figures, 2 tables, accepted for publication in A&A

References in corpus (3)

• The SCUBA Legacy Catalogue: Continuum Objects Detected by SCUBA
• WFCAM, Spitzer-IRAC and SCUBA observations of the massive star forming region DR21/W75: I. The collimated molecular jets
• [Ne II] Observations of Gas Motions in Compact and Ultracompact H II Regions

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• The magnetic field in the dense photodissociation region of DR 21
• Gas Kinematics in the HII regions G351.69-1.15 and G351.63-1.25
• ASKAP EMU Radio Detection of the Reflection Nebula VdB-80 in the Monoceros Crossbones Filamentary Structure
• NGC 7538 IRS2 in [NeII]: Shell and Cavity Kinematics of a Compact HII Region
• The ultracompact regions G40.54+2.59 and G34.13+0.47: A new detection of compact radio sources
• The Cygnus Allscale Survey of Chemistry and Dynamical Environments: CASCADE III. The large scale distribution of DCO+, DNC and DCN in the DR21 filament