The origin of a chemically enriched Lyα absorption system at z=0.167

We present the first detailed analysis of the chemical abundances, ionization state, and origin of a partial Lyman limit system [N(H I) approximate to 10(16) cm(-2)] at low redshift (z = 0.167 toward PKS 0405-1219). Two galaxies at an approximate to 70 h(-1) kpc projected distance to the QSO have been identified at the absorber redshift. We analyze an echelle spectrum of the QSO obtained with the Space Telescope Imaging Spectrograph and find that this absorption system exhibits associated lines produced by C+, N+, O-0, Si+, Si++, Si+3, Fe+, and Fe++ and, most interestingly, O+5 and N+4. Th, results of our analysis show that the partial Lyman limit system traced by various ions is likely to be embedded in a collisionally ionized O VI gas of larger spatial extent. Furthermore, the partial Lyman limit system appears to have a metallicity of at least 1/10 solar and is most likely solar or supersolar despite the fact that no luminous galaxies are seen within a projected distance rho = 60 h(-1) kpc to the QSO. Finally, adopting the temperature estimated for the hot gas (T approximate to 2.5 x 10(5) K) and assuming a simple isothermal halo, we estimate that the galaxy or galaxy group that supports the extended gas may have a total mass approximate to1.5 x 10(12) Mo and a gas number density less than or similar to3 x 10(-5) cm(-3).