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| Paper: |
Multi-phase High-Velocity Clouds toward HE 0226 4110 |
| Volume: |
348, Astrophysics in the Far Ultraviolet: Five Years of Discovery with FUSE |
| Page: |
385 |
| Authors: |
Fox, A.J.; Savage, B.D.; Wakker, B.P.; Tripp, T.M.; Sembach, K.R. |
| Abstract: |
O VI absorption in high-velocity clouds has been detected with the FUSE satellite in many directions across the sky. We discuss the ionization conditions and kinematics of a high positive-velocity absorption system toward the Seyfert 1 galaxy HE 0226–4110, for which high-quality FUSE and STIS data are available. In this sightline, the high-velocity O VI is accompanied by absorption in several neutral and weakly ionized species over the same velocity range, vLSR = 55–230 km s−1. We apply CLOUDY modeling to determine whether photoionization is a feasible ionization mechanism in these clouds, assuming that they are bathed in the extragalactic radiation field. Photoionization can account for the observed column densities of C II, C III, Si II, and Si III if the clouds are several kpc in depth, but cannot explain the columns of C IV or O VI. Analysis of the absorption kinematics and high-ion column density ratios leads us to conclude that the highly ionized species originate in conductive interfaces at the surface of warm HVCs, which are embedded in a hot exterior medium. This hot medium is probably the highly extended Galactic corona that has been invoked to explain X-ray observations of O VII and O VIII absorption. |
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