UBC Theses and Dissertations
Two HII/HI complexes in the outer galaxy Wall, William Frank
The HII regions S211 and S212 have been observed at 1420MHz, in both line and continuum, using the synthesis telescope at the Dominion Radio Astrophysical Observatory. S211 and S212 and their associated atomic hydrogen were studied as part of an ongoing investigation of HII/HI complexes within molecular clouds. S211 and S212 both require a flux of ionizing photons consistent with the ultraviolet emission from an 06V star. S211 was barely resolved (1.6 beam widths) and was thus modelled with a constant density model with density 85cm⁻³. S212 was modelled with linear density gradients and a central density of 50 cm⁻³. S212 is probably density bounded towards the east and south. There is evidence for S212 and indirect evidence for S211 to suggest that both HII regions contain unresolved clumps of enhanced density. This would imply young ages (< 10⁵ yrs) for both HII regions. S211 was found to have 4000 M© of associated HI, roughly hemispherical in shape and extending 20 pc from the major ionizing star of S211. S212 possesses 1200 M© of atomic hydrogen which reaches an extent of 20 pc from its major ionizing star. Neither HI region would easily conform to a steady state photodissociation model assuming uniform hydrogen density. This is undoubtedly due to the young age of the HII regions as well as to a gradient in the gas density.
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