330-MHz radio continuum imaging of the W51 complex

Abstract

We present a 1.1-arcmin-resolution image of the W51 complex made with the Very Large Array at a frequency of 330 MHz. W51A and W51B are resolved into multiple components at metre wavelengths for the first time: most of the compact components have spectra that are self-absorbed at this low observing frequency and these components appear surrounded by thermal plasmas with low emission measures. We estimate the electron temperature towards the brightest subcomponent of W51A (G49.5–0.4e) to be >7500 K. This temperature estimate is consistent with inferences from observations of radio recombination lines from the H II region: there is no evidence in our image for a radial temperature decrement within the subcomponent.