Revealing the Galactic H II Region G84.9+0.5 through 5 GHz Continuum and Polarization Emission and a Voigt Profile Analysis of Radio Recombination Line Observations

摘要

We present new λ = 6 cm radio observations (Stokes I, Q, and U and hydrogen recombination line) of the Galactic object G84.9+0.5, previously classified as a supernova remnant. Radio recombination line (RRL) emission near 6 cm is detected in deep GBT observations, and we are able to separate the 7.6 mK line detected from this object (appearing at vLSR = -40 km s-1) from the line emitted by ionized gas of W80 in the foreground (Tl = 5.4 mK; vLSR ~ 0 km s-1) along the same line of sight (LOS). Detection of RRL emission from G84.9+0.5 and the absence of polarized emission at 6 cm imply that this object is an H II region. Rather than a Gaussian, a Voigt function better describes the extended line profile of G84.9+0.5, which has a low-level "wing" extending into its negative-velocity end. A Monte Carlo analysis of noisy synthetic spectra is presented, and it is concluded the wing is not spurious. Two physical explanations for the wing (pressure broadening and an outflow of gas) are considered. We favor that of a champagne-type outflow in the gas flowing along the inside wall of a known molecular cloud in the vicinity of the nebula (at -40 km s-1), making G84.9+0.5 a "blister" type H II region viewed face-on. We find Te = 9900 K and ne = 20 cm-3 from a non-LTE analysis of the peak toward the RRL, and a total H II mass of 440 M☉. A distance of 4.9 kpc is determined for this object. An IR analysis using MSX and 2MASS data is presented, showing H II region colors for G84.9+0.5 and identifying a possible exciting star for this H II region.