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

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) × 10 14 cm -2 . By combining emission- and absorption-line data for this sight line, we estimate the physical parameters of the emitting gas.