FUSE Detection of Diffuse Galactic O VI Emission toward the Coma and Virgo Clusters

Abstract

We report the detection of diffuse O VI 1032, 1038 A emission in a 29-ksec observation centered on the Coma Cluster (l = 57.6, b = +88.0) and an 11-ksec observation toward Virgo (l = 284.2, b = +74.5) through the low-resolution (30"x30") 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/cm2/s/sr for each of the O VI components in the Coma spectrum and 2900 +/- 700 and 1700 +/- 700 photons/cm2/s/sr for the 1032 and 1038 A 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 ksec 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.