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Paper: A Search for O VI Emission from High Velocity Clouds
Volume: 348, Astrophysics in the Far Ultraviolet: Five Years of Discovery with FUSE
Page: 391
Authors: Benjamin, R.A.; Wakker, B.P.; Otte, B.; Dixon, W.V.
Abstract: We have searched for OVI emission associated with OVI absorption produced by high velocity clouds along the lines of sight to two extragalactic sources: NGC 7714 (behind the Magellanic Stream) and PG 1626+554 (behind Complex C). We obtained 2963 upper limits for O VI emisison line fluxes of 1700 and 1000 photons s−1 cm−2, respectively. Along the same sightlines, we have dectected high velocity O VI absorption with a column density of NHV C = 1014.45 and 1014.15. Assuming this gas is in ionization equilibrium at T = 105.5 K with solar metallicity, the inferred hydrogen density is nH < 10−2.4, cm−3 and < 10−2.5 cm−3, and the corresponding limits on the thermal pressure in the O VI bearing zone are (p/k) < 1100 cm−3 K around the Magellanic Stream and (p/k) < 1260 cm−3 K around Complex C. We discuss the implications of these measurements for constraining the density and pressure of the gaseous Galactic halo at the distances of these two HVCs and the source of ionizing fluxes on HVCs inferred from Hα measurements.
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