Radio continuum and radio recombination line observations of W51

Radio continuum observations at 3.6, 6, and 20 cm of W51 A (G49.5-0.4) have been carried out using the Very Large Array (VLA) in the C and D configurations. The maximum resolution is 3 sec. The goals of this study were to determine the spectra of the individual components and to derive the physical parameters of the gas, such as the electron number density and emission measure. A number of other sources in the W51 complex, including G49.4-0.3, were included in the 20 cm primary beam. Several new H II regions were detected. An H92(alpha) (8.3 GHz) radio recombination line (RRL) observation was also carried out using the C configuration of the VLA with an angular resolution of 3 sec. The goals of the RRL observation were to determine the kinematics and the electron temperature of the ionized gas as well as the abundance of singly ionized helium relative to ionized hydrogen. The results of this study indicate that most of the ionized gas in G49.5-0.4 has velocities in the range 40 to 80 km/sec. However, there is some gas in a compact region (source d1 at a velocity of -41 km/sec. If this region is in circular rotation about the Galactic center, it is located 15 kpc from the Sun. Another possibility is that d1 is a shell-like structure that is being viewed edge on and the near side is expanding toward the observer at 80 km/sec. Derived LTE electron temperatures are in the range of 4500 to 11,000 K with a mean of 7800 +/- 1200 K. The ionized helium abundance is 0.096 +/- 0.015.