THE CONNECTION BETWEEN A LYMAN LIMIT SYSTEM, A VERY STRONG O vi ABSORBER, AND GALAXIES AT z ∼ 0.203

With a column density log N(O vi) = 14.95 ± 0.05, the O vi absorber at zabs ≃ 0.2028 observed toward the quasi-stellar object PKS 0312–77 (zem = 0.223) is the strongest yet detected at z < 0.5. At nearly identical redshift (zabs ≃ 0.2026), we also identify a Lyman limit system (LLS, log N(H i) = 18.22+0.19−0.25). Combining FUV and NUV spectra of PKS 0312–77 with optical observations of galaxies in the surrounding field (15′ × 32′), we present an analysis of these absorbers and their connection to galaxies. The observed O i/H i ratio and photoionization modeling of other low ions indicate that the metallicity of the LLS is [Z/H]LLS ≃ −0.6, and that the LLS is nearly 100% photoionized. In contrast, the O vi-bearing gas is collisionally ionized at T ∼ (3–10) × 105 K as derived from the high-ion ratios and profile broadenings. Our galaxy survey reveals 13 (0.3 ≲ L/L* ≲ 1.6) galaxies at ρ < 2h−170 Mpc and |δv| ≲ 1100 km s−1 from the LLS. A probable origin for the LLS is debris from a galaxy merger, which led to a 0.7 L* galaxy ([Z/H]gal ≃ +0.15) at ρ ≃ 38h−170 kpc. Outflow from this galaxy may also be responsible for the supersolar ([Z/H]abs ≃ +0.15), fully ionized absorber at zabs ≃ 0.2018 (−190 km s−1 from the LLS). The hot O vi absorber likely probes coronal gas about the 0.7 L* galaxy and/or (∼0.1 keV) intragroup gas of a spiral-rich system. The association of other strong O vi absorbers with LLS suggests that they trace galactic and not intergalactic structures.