Ultracompact HiiRegions with Extended Radio‐Continuum Emission

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Abstract
We have conducted a 3.6 cm radio-continuum survey with the VLA in its compact D-array to look for extended radio-continuum emission around known ultracompact H II regions. We find extended emission in 12 out of 15 fields. The extended emission ranges in size up to 5', with typical diameters of 60'', or 2 pc. In some cases, the extended component produces an order of magnitude more flux than the ultracompact component. It is possible that the extended emission is from H II regions not connected with the ultracompact H II regions, but on the basis of the morphology of the emission, we believe that it is possible or even likely that the ultracompact and extended emission are directly connected in about half of the sources. The possible consequences of directly connected extended emission are profound. We may be forced to reconsider the definition of an ultracompact H II region and consider models in which dense, ultracompact ionized components are embedded in less dense, more extended regions.

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