VLA H92 alpha and H115 beta recombination line observations of the Galactic center H II regions: The Sickle (G0.18-0.04) and the Pistol (G0.15-0.05)

The Very Large Array has been used in the CnB and DnC configurations to observe the remarkable Galactoc center sources, the Sickle and the Pistol, near l = 0 degrees.18, b = -0 degrees.04. These H II regions have an unusual morphology and may be physically associated with the linear nonthermal filaments at l - 0.18, which appear to intersect the sources. The H92 alpha (8.31 GHz) and H115 beta (8.43 GHz) radio recombination lines arising from these sources have been observed with angular resolutions of 6'' and 9'', respectively. In addition, there is a probable detection of the helium line in the Pistol (Y+ similar to 14% +/- 6%), while in the Sickle, no helium lines were detected with an upper limit of Y+ similar to 5% (3 sigma). A complex velocity field has been observed in both sources. The LSR velocity in the Sickle varies from 0 to 75 km s(-1) with an average velocity of similar to 35 km s(-1); the average velocity of the Pistol is similar to 115 km s(-1). The recombination line properties of the Sickle and the Pistol (FWHM line widths, line-to-continuum ratios, beta-to-alpha ratio) are consistent with photoionization from hot stars. The beta-to-alpha line ratio of similar to 0.35 +/- 0.07 over most of the Sickle and Pistol does nut differ significantly from the LTE value of 0.28. The average LTE electron temperature, T-e*, for the Sickle (similar to 5500 K) is similar to typical Galactic center H II regions, and T-e* for the Pistol is somewhat lower (similar to 3600 K). An additional H II component in the line profiles of three legions of the Sickle in which the nonthermal filaments are present suggests that an interaction between the ionized gas and the nonthermal filaments is occurring. The probable detection of He92 alpha in the Pistol and the nondetection in the Sickle may be due to a difference in the radiation field of the ionizing sources.