Far Ultraviolet Spectroscopic Explorer Observations of O VI in High-Velocity Clouds

Details Far Ultraviolet Spectroscopic Explorer Observations of O VI in High-Velocity Clouds Far Ultraviolet Spectroscopic Explorer Observations of O VI in High-Velocity Clouds

Jul 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000apj...538l..31s&link_type=abstract

The Astrophysical Journal, Volume 538, Issue 1, pp. L31-L34.

Astronomy and Astrophysics

Astronomy

70

Galaxy: Halo, Galaxies: Intergalactic Medium, Ism: Clouds, Ism: Evolution, Ism: Kinematics And Dynamics, Ultraviolet: Ism

Scientific paper

We have used moderate-resolution (FWHM ~ 25 km s-1) spectra of active galactic nuclei and QSOs observed by the Far Ultraviolet Spectroscopic Explorer to make the first definitive measurements of absorption by hot gas in high-velocity clouds (HVCs) at large distances from the Galactic plane. Seven of the 11 sight lines studied exhibit high-velocity (VLSR>100 km s-1) O VI λ1031.93 absorption with logN(O VI)~13.79-14.62. High-velocity O VI absorption is detected in the distant gas of H I HVC complex C, the Magellanic Stream, several HVCs believed to be in the Local Group, and the outer Galaxy. The fraction of O VI in HVCs along the seven sight lines containing high-velocity O VI averages ~30%, with a full range of ~10%-70%. The O VI detections imply that hot (T~3×105 K), collisionally ionized gas is an important constituent of the HVCs since O VI is difficult to produce by photoionization unless the path lengths over which the absorption occurs are very large (>100 kpc). The association of O VI with H I HVCs in many cases suggests that the O VI may be produced at interfaces or mixing layers between the H I clouds and hot, low-density gas in the Galactic corona or Local Group. Alternatively, the O VI may originate within cooling regions of hot gas clouds as they are accreted onto the Galaxy.

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