The multiphase intergalactic medium toward PKS 2155-304

We study the cluster of H I and O vi absorption systems and the claimed detection of O VIII absorption from the intergalactic medium at z approximate to 0.0567, associated with a group of galaxies toward the BL Lac object PKS 2155 - 304. As measured by spectrographs on the Hubble Space Telescope, Far Ultraviolet Spectroscopic Explorer, and Chandra, this system appears to contain gas at a variety of temperatures. We analyze this multiphase gas in a clumpy-infall model. From the absence of C IV and Si III absorption in the Lyalpha clouds, we infer metallicities less than 2.5% - 10% of solar values. The only metals are detected in two O vi absorption components, offset by +/- 400 km s(-1) from the group barycenter (cz approximate to 16,000 km s(-1)). The O vi components may signify nearside and backside infall into the group potential well, which coincides with the claimed O VIII absorption. If the claimed O VIII detection is real, our analysis suggests that clusters of strong Lya and O vi absorbers, associated with groups of galaxies, may be the signposts of shock-heated metal-enriched baryons. Through combined UV and X-ray spectra of H I and O VI, O vVII, and O VIII, one may be able to clarify the heating mechanism of this multiphase gas.