GHRS and ORFEUS-II Observations of the Highly Ionized Interstellar Medium Toward ESO141-055

We present Goddard High Resolution Spectrograph and ORFEUS-II measurements of Si IV, C IV, N V, and O VI absorption in the interstellar medium of the Galactic disk and halo toward the nucleus of the Seyfert galaxy ESO141-055. The high ionization absorption is strong, with line strengths consistent with the spectral signature expected for hot (T ∼> 10 5 K) collisionally ionized gas in either a “Galactic fountain” or an inhomogeneous medium containing a mixture of conductive interfaces and turbulent mixing layers. The total O VI column density of ≈ 10 cm suggests that the scale height of O VI is large (∼>3 kpc) in this direction. Models of the C IV velocity distribution along the sight line are consistent with a large scale height for the highly ionized gas. Comparison of the high ion column densities with measurements for other sight lines indicates that the highly ionized gas distribution is patchy. The amount of O VI perpendicular to the Galactic plane varies by at least a factor of ∼ 4 among the complete halo sight lines thus far studied. In addition to the high Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555.