A VLA H92α Recombination Line Study of the Arched Filament H [CSC]ii[/CSC] Complex Near the Galactic Center

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Abstract
The Very Large Array has been used at 8.3 GHz in the DnC and CnB array configurations to carry out an H92α recombination line study of the ionized gas in the Arched Filaments H II complex, which defines the western edge of the Galactic center Radio Arc. The Arched Filaments consist of a series of curved filamentary ridges which extend over 9' × 6' (22 × 16 pc) and are intersected in two places by linear, nonthermal, magnetic filaments. The H92α observations cover the entire Arched Filaments region using a four-field mosaic, with an angular resolution of 128 × 810; an additional higher resolution (36 × 27) field was imaged in the SW portion of the H II complex. High-resolution continuum images are also presented. The H92α line properties of the ionized gas (line-to-continuum ratio, FWHM line width, T) are consistent with photoionization from hot stars and consistent with the physical properties of other Galactic center H II regions. The LTE electron temperatures vary only slightly across the entire extent of the source and have an average value of 6200 K. The velocity field is very complex, with velocities ranging from +15 to -70 km s-1 and the majority of velocities having negative values. Large velocity gradients (2–7 km s-1 pc-1, with gradients in some regions larger than 10 km s-1 pc-1) occur along each of the filaments, with the velocities becoming increasingly negative with decreasing distance from the Galactic center. The negative velocities and the sense of the velocity gradients can be understood in terms of the orbital path of the underlying molecular cloud about the Galactic center. The magnitudes of the velocity gradient are consistent with the cloud residing on an inner, elongated orbit which is due to the Galaxy's stellar bar, or with a radially infalling cloud. The ionization of the Arched Filaments can be accounted for completely by the massive Arches stellar cluster, which consists of more than 150 O stars and produces a few ×1051 photons s-1. This cluster is likely to be located 10–20 pc from the Arched Filaments, which can explain the uniformity of ionization conditions in the ionized gas.
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