Anomalous Motion of Ionized Gas in the Sickle (G0.18--0.04) Near the Galactic Center

Abstract

We present VLA measurements of H92alpha radio recombination line emission from an unusual HII region G0.18--0.04, the ``Sickle'', with spatial and spectral resolutions of 27" times 24".9 and 14 km/s, respectively. These observations detected two new kinematic components of ionized gas whose velocities differ greatly from the +25 km/s molecular cloud surrounding the Sickle. One component is highly red-shifted with peak velocity of about +150 km/s and the other is a blue-shifted velocity feature peaking near -35 km/s. Neither of these high-velocity features have molecular counterparts. The blue-shifted feature is forbidden in the sense of Galactic rotation and coincides with the prominent nonthermal filaments crossing the Sickle, thus suggesting that they are physically associated with each other. The results presented here are interpreted in terms of ionized gas being accelerated away from the surface of the cloud associated with the Sickle region, either by the magnetic field associated with the nonthermal filaments or by the stellar winds from the hot helium stars near G0.18--0.04.