Far-Ultraviolet Spectroscopic Explorer detection of diffuse Galactic OVI emission toward the Coma and Virgo Clusters

We report the detection of diffuse O VI lambda lambda 1032, 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" x 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 2038 Angstrom 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 similar to 200 ks FUSE observation. From a FUSE spectrum of M87, we find that N(O VI) toward Virgo is (1.4 +/- 0.8) x 10(14) cm(-2). By combining emission- and absorption-line data for this sight line, we estimate the physical parameters of the emitting gas.