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

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 (1032,1038 A) and C IV (1548,1551 A). We do not detect significant emission from either species in any of the spectra. Lieu et al. [ApJ, 458, L5 (1996)] have recently proposed a warm [(5-10) * 10^5 K] component to the intracluster medium (ICM) to explain the 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 500,000 K gas in the center of the Virgo cluster. This inconsistency may be alleviated if the central gas temperature is >= 750,000 K. HUT limits on the O VI surface brightness of the four other clusters can provide important constraints on models of their ICM.