Limits on Far-Ultraviolet Emission from Warm Gas in Clusters of Galaxies with the Hopkins Ultraviolet Telescope

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Abstract
We have searched the far-UV spectra of five clusters of galaxies observed with the Hopkins Ultraviolet Telescope (HUT) for emission in the resonance lines of O VI λλ1032, 1038 and C IV λλ1548, 1551. We do not detect significant emission from either species in any of the spectra. Lieu et al. have recently proposed a warm [(5-10) × 105 K] component to the intracluster medium (ICM) to explain excess 0.065-0.245 keV flux present in EUVE and ROSAT observations of the Virgo cluster. If the surface brightness of this warm component follows that of the hot, X-ray-emitting gas (i.e., is centrally condensed), then our upper limit to the O VI surface brightness in M87 is inconsistent with the presence of substantial 5 × 105 K gas in the center of the Virgo cluster. This inconsistency may be alleviated if the central gas temperature is 7.5 × 105 K. HUT limits on the O VI surface brightness of the four other clusters can provide important constraints on models of their ICM.
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