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

摘要

We have searched the far-UV spectra of five clusters of galaxies observedwith the Hopkins Ultraviolet Telescope (HUT) for emission in the resonancelines of O VI (1032,1038 A) and C IV (1548,1551 A). We do not detectsignificant 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] componentto the intracluster medium (ICM) to explain the excess 0.065-0.245 keV fluxpresent in EUVE and ROSAT observations of the Virgo cluster. If the surfacebrightness 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 surfacebrightness in M87 is inconsistent with the presence of substantial 500,000 Kgas in the center of the Virgo cluster. This inconsistency may be alleviated ifthe central gas temperature is >= 750,000 K. HUT limits on the O VI surfacebrightness of the four other clusters can provide important constraints onmodels of their ICM.