Multifrequency, High-Resolution Radio Recombination Line Observations of the Massive Star-forming Region W49A

摘要

We have carried out a multifrequency, multiconfiguration VLA observational program of the massive Galactic star-forming region W49A (D = 11.4 kpc). Radio continuum observations were carried out at 0. 7, 1.3, and 3.6 cm. In the highest sensitivity 3.6 cm images, we have detected 45 distinct continuum sources (located within a ～4' [13 pc] diameter region) exhibiting a wide variety of sizes and morpho- logical types. Several sources have rising continuum spectra (α > 0.6) up to the shortest wavelengths observed (7 mm). We observe a larger fraction of sources with shell morphologies (11/100) than were observed in the Galactic plane survey of Wood & Churchwell. A correlation between the rms electron density and the radius of the ultracompact H II regions is observed for the spherical, unresolved, and cometary sources in W49A.