[ITAL]Far-Ultraviolet Spectroscopic Explorer[/ITAL] Detection of Diffuse Galactic O [CSC]vi[/CSC] Emission toward the Coma and Virgo Clusters

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Abstract
We report the detection of diffuse O VI λλ1032, 1038 emission in a 29 ks observation centered on the Coma Cluster (l = 57.6, b = +88.0) and an 11 ks observation toward Virgo (l = 284.2, b = +74.5) through the 30'' × 30'' aperture of the Far-Ultraviolet Spectroscopic Explorer (FUSE). The emission lines have a redshift near zero and are thus produced by gas in our own Galaxy. Observed surface brightnesses are 2000 ± 600 photons cm-2 s-1 sr-1 for each of the O VI components in the Coma spectrum and 2900 ± 700 and 1700 ± 700 photons cm-2 s-1 sr-1 for the 1032 and 1038 Å lines, respectively, toward Virgo. These features are similar in strength to those recently observed in the southern Galactic hemisphere (l = 315.0, b = -41.3) in an ~200 ks FUSE observation. From a FUSE spectrum of M87, we find that N(O VI) toward Virgo is (1.4 ± 0.8) × 1014 cm-2. By combining emission- and absorption-line data for this sight line, we estimate the physical parameters of the emitting gas.
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