VLA Radio Recombination Line Observations of Ionized Gas in the -30 Kilometers per Second Molecular Cloud (G0.04+0.03) near the Galactic Center. I. The Discrete Radio Sources
Multifrequency spectral line and continuum observation of ionized gas in the -30 km s-1 molecular cloud (G0.04+0.03) have been carried out using the VLA to study the nature of the discrete radio sources located between Sgr A West (l = 0°) and the arched filaments of the continuum arc (l = 0°.2). Spectral indices determined from 6 and 20 cm continuum data indicate that the spectra of these sources are flat or rising with frequency. Radio morphologies and the detection of radio recombination lines (H110α and H92α) confirm that these sources are H II regions. The line emission arises at negative radial velocities (-60 to -20 km s-1), forbidden at these longitudes in the sense of Galactic rotation. The kinematics of the ionized gas suggest a close relationship with the molecular cloud observed in CS and 13CO at a mean radial velocity of -30 km s1 (G0.04+0.03). We derive LTE electron temperatures in the range 3500-7200 K. The low inferred electron temperatures may indicate relatively high metal abundances in these regions. The thermal sources are spatially correlated with [C II] 158 microns emission peaks and with the distribution of warm dust as indicated by the color temperature, Tc(55/125 μm). Overall, their properties and environments indicate that these H II regions are ionized by UV radiation from recently formed early-type stars in the molecular cloud at -30 km s-1.