VLA H92 alpha and H115 beta Recombination Line,Observations of the Galactic Center H II Regions:,The Sickle (G0.18-0.04) and Pistol (G0.15-0.05)

Cornelia C. Lang(1),W.M. Goss(2), D.O.S Wood(2,3)

(1) Vassar College Observatory, Poughkeepsie, NY 12601. Current address: Department of Astronomy, 8979 Math Sciences Building, UCLA, Los Angeles, CA 90095-1562; email: clang@eggneb.astro.ucla.edu (2) National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (3) Kodak Scientific Imaging Systems, 4 Science Park, New Haven, CT 06511

Paper: to appear in ApJ, 1 Jan 1997


The Very Large Array has been used in the CnB and DnC configurations to observe the remarkable Galactic Center sources, the Sickle and Pistol, near l =0.^o18 b=-0.^o04. These HII regions have an unusual morphology and may be physically associated with the linear non-thermal filaments at l =0.^o18 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^+~14+/-6%), while in the Sickle, no helium lines were detected with an upper limit of Y^+~ 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/sec , with an average velocity of ~35 km/sec ; the average velocity of the Pistol is ~115 km/sec . The recombination line properties of the Sickle and 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 ~0.35+/-0.07 over most of the Sickle and Pistol does not differ significantly from the LTE value of 0.28. The average LTE electron temperature, T_e^*, for the Sickle (~5500 K) is similar to typical Galactic Center HII regions, and T_e^* for the Pistol is somewhat lower (~3600 K). An additional HII component in the line profiles of three regions of the Sickle in which the non-thermal filaments are present suggests that an interaction between the ionized gas and the non-thermal filaments is occuring. The probable detection of He92 alpha in the Pistol and the non-detection in the Sickle may be due to a difference in the radiation field of the ionizing sources.

Preprints available from the authors at clang@astro.ucla.edu , or the raw TeX (no figures) if you click here.

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