We present analyses of the physical conditions in the z ( \hbox { { O~ { } } \kern 1.0 pt { \sc vi } } ) = 0.22496 and z ( \hbox { { O~ { } } \kern 1.0 pt { \sc vi } } ) = 0.22638 multi-phase absorption systems detected in the ultraviolet HST/ 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 \sim 2 L _ { B } ^ { * } Sbc-Sc galaxy situated at a projected distance of \sim 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 \lesssim 3 \times 10 ^ { 4 } K. The low and intermediate ions in this absorber are consistent with an origin in a T \sim 10 ^ { 4 } K photoionized gas with [ Si/H ] and [ C/H ] of \sim - 0.6 dex .
In contrast , the broader O vi absorption is likely produced in collisionally ionized plasma under nonequilibrium conditions .
The z ( \hbox { { O~ { } } \kern 1.0 pt { \sc vi } } ) = 0.22638 system has broad Ly \alpha ( BLA ) and C iii absorption offset by v = -53 km s ^ { -1 } from O vi .
The H i and C iii line widths for the BLA imply T = 1.1 \times 10 ^ { 5 } K. For non-equilibrium cooling we obtain [ C/H ] \sim - 1.5 dex and N ( \hbox { { H } } ) = 3.2 \times 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 \sim 3 \times 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 \sim 10 ^ { 5 } K ) at the interface layers between the warm ( T < 5 \times 10 ^ { 4 } K ) HVC gas phase and the hot ( T \gtrsim 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 .