The Connection Between a Lyman Limit System, a Very Strong O VI Absorber, and Galaxies at z ~ 0.203

Abstract

With a column density log N(O VI) = 14.95 ± 0.05, the O VI absorber at z _abs sime 0.2028 observed toward the quasi-stellar object PKS 0312-77 (z _em = 0.223) is the strongest yet detected at z < 0.5. At nearly identical redshift (z _abs sime 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 sime -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 lsim L/L _* lsim 1.6) galaxies at ρ < 2h ^-1 ₇₀ Mpc and |δv| lsim 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 sime +0.15) at ρ sime 38h ^-1 ₇₀ kpc. Outflow from this galaxy may also be responsible for the supersolar ([Z/H]_abs sime +0.15), fully ionized absorber at z _abs sime 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.

Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer (FUSE). FUSE is operated for NASA by the Johns Hopkins University under NASA contract NAS5-32985. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract No. NAS5-26555.