Ultracompact H II Regions with Extended Emission: The Complete View
Abstract
In this paper we present the results of a morphological study performed on a sample of 28 ultracompact ~located near extended free-free emission, using radio continuum observations at 3.6~cm with the C and D VLA~configurations, with the aim of determining a direct connection between them. By using previously published observations in B and D VLA~configurations, we compiled a final catalogue of 21 ultracompact ~directly connected with the surrounding extended emission. The observed morphology of most of the ultracompact ~in radio continuum emission is irregular (single or multi-peaked sources) and resembles a classical bubble structure in the Galactic plane with well-defined cometary arcs. Radio continuum images superimposed on colour composite Spitzer images reinforce the assignations of direct connection by the spatial coincidence between the ultracompact components and regions of saturated 24~~emission. We also find that the presence of extended emission may be crucial to understand the observed infrared-excess because an underestimation of ionizing Lyman photons was considered in previous works.
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