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 610–1150 Å , 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 vi \lambda \lambda 1031 , 1037 apparent column density profiles reveals no evidence for partial coverage or unresolved saturated structure , although parts of the O vi \lambda 1037 line are blended with Galactic C iv absorption .
In addition , several transitions ( e.g , C iii \lambda 977 , H i Ly- \beta ) 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 } ^ { +0.16 } , \log U = -2.29 _ { -0.23 } ^ { +0.02 } .
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 km s ^ { -1 } 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 \lesssim \log U \lesssim 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 .