HIGHLY IONIZED PLASMA IN THE HALO OF A LUMINOUS SPIRAL GALAXY NEAR z=0.225

We present analyses of the physical conditions in the z(O VI) = 0.22496 and z(O VI) = 0.22638 multiphase absorption systems detected in the ultraviolet Hubble Space Telescope/STIS and FUSE spectra of the quasar H 1821+643 (m(V) = 14.2, z(em) = 0.297). Both absorbers are likely associated with the extended halo of a similar to 2L(B)* Sbc-Sc galaxy situated at a projected distance of similar to 116 h(71)(-1) kpc from the sight line. The z = 0.22496 absorber is detected in C II, C III, C IV, O III, O VI, Si II, Si III, and H I (Ly alpha-Ly theta) at > 3 sigma significance. The components of Si III and Si II are narrow with implied temperatures of T less than or similar to 3 x 10(4) K. The low and intermediate ions in this absorber are consistent with an origin in a T similar to 10(4) K photoionized gas with [Si/H] and [C/H] of similar to -0.6 dex. In contrast, the broader O VI absorption is likely produced in collisionally ionized plasma under nonequilibrium conditions. The z(O VI) = 0.22638 system has broad Ly alpha (BLA) and C III absorption offset by nu = -53 km s(-1) from O VI. The H I and C III line widths for the BLA imply T = 1.1 x 10(5) K. For non-equilibrium cooling we obtain [C/H] similar to -1.5 dex and N(H) = 3.2 x 10(18) cm(-2) in the BLA. The O VI, offset from the BLA with no detected H I or C III, is likely collisionally ionized at T similar to 3 x 10(5) K. From the observed multiphase properties and the proximity to a luminous galaxy, we propose that the z = 0.22496 absorber is an extragalactic analog of a highly ionized Galactic HVC, in which the O VI is produced in transition temperature plasma (T similar to 10(5) K) at the interface layers between the warm (T < 5 x 10(4) K) HVC gas phase and the hot (T greater than or similar to 10(6) K) coronal halo of the galaxy. The z = 0.22638 O VI-BLA absorber could be tracing a cooling condensing fragment in the nearby galaxy's hot gaseous halo.