X–ray absorption lines in FUV–detected quasars: I. Sample and analysis of the XMM–Newton and Chandra data

This paper presents initial results of a systematic search for resonance X–ray absorption lines from H–like O VIII and He–like O VII caused by the intervening warm–hot intergalactic medium (WHIM). The search is based on far ultra–violet redshift priors from O VI and H I broad Lyman-α lines that were previously detected by HST and FUSE in a sample of 51 sources with either XMM-Newton or Chandra data, for a total X–ray redshift path of Δz = 10.9. Of the 1,224 absorption–line systems with FUV priors that were analyzed, 33 systems feature an absorption–line feature detected with ≥99 % confidence at the same redshift of the FUV prior, some coincident with previously reported absorption line detections. The ultimate goal of this search is to test the hypothesis that X–ray absorbing WHIM gas is the repository of the missing baryons in the local universe. Further results and the cosmological implications of this analysis are presented in a companion paper.