High - Resolution Absorption Spectroscopy of Multi - Phase , High - Metallicity Gas Associated with the Luminous Quasar He 0226 - 4110 ∗

We present FUSE and HST/STIS observations of the absorption line system near the emission redshift of the radio-quiet, X-ray bright quasar HE0226-4110 (z = 0.495, V = 15.2). The spectra cover the rest-frame wavelength range 610–1150Å, and we detect a wide range of ionization species, including four adjacent stages of oxygen: O III, O IV, O V, and O VI. Strong transitions of O I and O II are covered in our spectra, but none are detected. The detection of multiple ionization stages of a common element (oxygen) reveals a striking change in gas kinematics with ionization. Comparison of the O VIλλ1031, 1037 apparent column density profiles reveals no evidence for partial coverage or unresolved saturated structure, although parts of the O VIλ1037 line are blended with Galactic C IV absorption. In addition, several transitions (e.g, C III λ977, H I Ly-β) show black saturation which also indicates no unocculted flux that may dilute the absorption profiles. O III is only detected in a narrow feature which is also traced by the H I and C III lines, suggesting that they arise in the same gas. Absorption at the same velocity is also present in other species (N IV, O IV-VI, S IV, and possibly Ne VIII), but the kinematics differ from the O III, implying production in separate gaseous phases. The combination of H I, O III, and C III column density measurements with limits on the amount of O II and O IV in this phase yield an estimate of both the photoionization parameter and metallicity: [O/H]= +0.12 −0.03, logU = −2.29 +0.02 −0.23. We discuss two possible locations for the gas in this associated absorption-line system: the narrow emission line region of the quasar, and the halo of the quasar host galaxy. An additional narrow component that is only detected in O VI appears 58 kms redward of the O III-bearing gas. The narrow width of this component rules out collision-based ionization processes, and we constrain the ionization parameter of this component to −0.35 . logU . 0.02. Additional structure is detected in the associated absorber in the form of two broad components. The components flank the narrow O III component in velocity and are detected in N IV, O IV-VI, and Ne VIII. The kinematics of O V and O VI in both components trace each other. The kinematics of N IV, O IV, and Ne VIII differ from O V and O VI and it is not clear how many phases or what ionization mechanism produces the gas in these broad components. A consideration of collisional ionization and photoionization equilibrium models, as well as radiative cooling and shock ionization models, leads us to conclude that Ne VIII must arise in a separate high-ionization phase. Subject headings: quasars: absorption lines — quasars: emission lines — quasars: individual (HE 0226-4110) — ultraviolet: ISM