HII regions, infrared dark molecular clouds and the local geometry of the Milky Way's nuclear star-forming ring

H. S. Liszt(1)

(1) National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA, USA 22903-2475

Paper: A&A, submitted 9 May 2009

EPrint Server: 0905.1412


Observations of the HII region-molecular cloud complexes Sgr B, C, D and E provide unique insights into the structure of a nuclear star-forming ring. To interpret the galactic center HII region/molecular cloud complexes as parts of a barred galaxy's nuclear star-forming ring. We compare observations of 18cm VLA radiocontinuumm, 8-22 mu MSX IR and 2.6mm BTL/KP12m CO emission from the Sgr B, C, D and E complexes in the inner few degrees of longitude. The observed IR structure and 8-22 mu IR source spectra are heavily influenced by extinction in individual compact HII regions and over entire source complexes: in the most striking case, the powerful compact HII regions in Sgr B2 at l > 0.6 DEGr are almost undetected by MSX. In a few especially favorable cases the IR extinction from individual galactic center molecular clouds is seen to be wavelength-independent. The kinematics of the HII regions are mostly rotational, as expected for a nuclear star-forming ring but with spectactular departures in Sgr B and Sgr C. Owing to high molecular column density and flattening of the extinction curve, the galactic center HII regions would likely be shrouded even if viewed from outside. Slight departures from circular motion and perfect alignment with the galactic equator allow the front (Sgr B) and rear (Sgr C) portions of the Galaxy's nuclear star-forming ring to be distinguished. Much of the volume interior to the ring may be somewhat hollow.

Preprints available from the authors at hliszt@nrao.edu , or the raw TeX (no figures) if you click here.

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