To explore the ionization conditions in highly-ionized absorbers at high redshift we have studied in detail two intervening O vi absorbers at z \approx 2 towards the quasar PKS 1448 - 232 , based on high ( R \approx 75 , 000 ) and intermediate ( R \approx 45 , 000 ) resolution optical VLT/UVES spectra .
We find that both absorption systems are composed of several narrow subcomponents with C iv /O vi Doppler-parameters b < 10 km s ^ { -1 } , typically .
This implies that the gas temperatures are T < 10 ^ { 5 } K and that the absorbers are photoionized by the UV background .
The system at z = 2.1098 represents a simple , isolated O vi absorber that has only two absorption components and that is relatively metal-rich ( Z \sim 0.6 solar ) .
Ioinization modeling implies that the system is photoionized with O vi , C iv , and H i coexisting in the same gas phase .
The second system at z = 2.1660 represents a complicated , multi-component absorption system with eight O vi components spanning almost 300 km s ^ { -1 } in radial velocity .
The photoionization modeling implies that the metallicity is non-uniform and relatively low ( \leq 0.1 solar ) and that the O vi absorption must arise in a gas phase different from that traced by C iv , C iii , and H i .
Our detailed study of the two O vi systems towards PKS 1448 - 232 shows that multi-phase , multi-component high-ion absorbers like the one at z = 2.1660 require a detailed ionization modeling of the various subcomponents to obtain reliable results on the physical conditions and metal-abundances in the gas .