Broad recombination line objects in W49 North on 600 AU scales

摘要

We present 7 mm observations of the W49 North (W49N) massive star forming region, made with the Very Large Array, that detect recombination line emission from individual ultracompact H II regions on 50 mas (600 AU) scales. These recombination line observations, together with multifrequency continuum imaging, indicate that 5 - 7 of the 18 ultracompact H II regions in the region are broad recombination line objects (BRLOs) as described by Jaffe & Martin-Pintado (1999). These BRLOs have both broad radio recombination lines (DeltaV > 60 km s(-1)) and rising radio spectra (S-nu proportional to nu(alpha)) with alpha > 0.4. The broad linewidths of the H52alpha lines at 7 mm are not likely due to pressure broadening, but instead to systematic motions of the ionized gas. A variety of models have been proposed to explain the long lifetimes of ultracompact H II regions, including the photoevaporated disk model of Hollenbach et al. ( 1994). This model at least qualitatively explains many features of some of the ultracompact H II regions observed at high resolution, including the broad recombination lines, rising spectra, and bipolar morphologies. We suggest that we may be observing the signatures of ionized winds from circumstellar disks in a subset of the W49N ultracompact sources. [References: 17]