The Molecular Counterpart of the Galactic Center Arched Filament HII Complex: OVRO Observations of the CS(2-1) Line

The Owens Valley Radio Observatory (OVRO) millimeter array was used to make observations of the CS(2-1) line (at 97.981 GHz) arising from the G0.07+0.04 region of the ``-30 km/s'' molecular cloud near the Galactic center with a spatial resolution of ~8". The ionized edges of this cloud forms the Arched Filament HII regions which are ionized by the adjacent Arches stellar cluster. The OVRO data were combined with single-dish data obtained at the 30-m IRAM telescope by Serabyn & Guesten (1987). A comparison of this CS(2-1) data and the H92alpha recombination line data of Lang, Goss & Morris (2001) reveals that the ionized and molecular gas are physically related, but that their velocities in this region differ by up to 35 km/s. This difference in velocity can be understood if the gas that gave rise to the G0.07+0.04 HII region has been fully ionized. An overall comparison of the molecular and ionized gas across the entire -30 km/s cloud based on the single dish CS(2-1) data and the H92alpha line data illustrates that such differences in velocity between the ionized and molecular gas are common and that the geometrical arrangement of these components is complicated. Much of the ionized gas resides on the near side (to the observer) of the molecular cloud; however, in several regions, some molecular material must lie in front of the HII region. The Arches stellar cluster therefore appears to be located in the midst of the molecular clouds such that some of the near-side cloud surfaces along our line of sight have not been exposed to the ionizing radiation.