The O vi Absorbers toward PG 0953+415: High-Metallicity, Cosmic-Web Gas Far from Luminous Galaxies

The spectrum of the low-redshift QSO PG0953+415 shows two strong, interveningO VI absorption systems. To study the nature of these absorbers, we have usedthe Gemini Multiobject Spectrograph to conduct a deep spectroscopic galaxyredshift survey in the 5' x 5' field centered on the QSO. This survey is fullycomplete for r' < 19.7 and is 73% complete for r' < 21.0. We find threegalaxies at the redshift of the higher-z O VI system (z = 0.14232) including agalaxy at projected distance rho = 155 kpc. We find no galaxies in the Geminifield at the redshift of the lower-z O VI absorber (z = 0.06807), whichindicates that the nearest galaxy is more than 195 kpc away or has L < 0.04 L*.Previous shallower surveys covering a larger field have shown that the z =0.06807 O VI absorber is affiliated with a group/filament of galaxies, but thenearest known galaxy has rho = 736 kpc. The z = 0.06807 absorber is notable forseveral reasons. The absorption profiles reveal simple kinematics indicative ofquiescent material. The H I line widths and good alignment of the H I and metallines favor photoionization and, moreover, the column density ratios imply ahigh metallicity: [M/H] = -0.3 +/- 0.12. The z = 0.14232 O VI system is morecomplex and less constrained but also indicates a relatively high metallicity.Using galaxy redshifts from SDSS, we show that both of the PG0953+415 O VIabsorbers are located in large-scale filaments of the cosmic web. Evidently,some regions of the web filaments are highly metal enriched. We discuss theorigin of the high-metallicity gas and suggest that the enrichment might haveoccurred long ago (at high z).