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 (|V_(LSR)| > 100 km s~(-1)) O Ⅵ λ1031.93 absorption with log N(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 x 10~5 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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机译：我们已使用中紫外光谱（FWHM≈25 km s〜（-1）），通过远紫外光谱浏览器观测到了活跃的银河核和QSO，从而首次确定了高速云（HVC）中热气体吸收的确定性量度。 ）与银河系飞机相距很远。所研究的11条视线中的7条视线表现出高速（| V_（LSR）|> 100 km s〜（-1））OⅥλ1031.93吸收，log N（OⅥ）≈13.79-14.62。在HⅠHVC络合物C，麦哲伦流，一些被认为是本地群的HVC和外星系中的遥远气体中检测到高速OⅥ吸收。沿高速视线的七个视线中HVC中OⅥ的比例平均为〜30％，全范围为〜10％-70％。 OⅥ检测表明，热的（T〜3 x 10〜5 K）碰撞离子化气体是HVC的重要组成部分，因为除非通过吸收发生的路径长度非常大，否则很难通过光电离产生OⅥ。 > 100 kpc）。 OⅥ与HⅠHVC的关联在许多情况下表明OⅥ可能在银云冠或局部群中HⅠ云与热的低密度气体之间的界面或混合层处产生。或者，OⅥ可能会在热气云积聚到银河系中时在热气云的冷却区域内产生。
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