The OVI absorbers toward PG 0953+415: High-metallicity, cosmic-web gas far from luminous galaxies

The spectrum of the low-redshift QSO PG 0953 + 415 (z(QSO) = 0.234) shows two strong, intervening O VI absorption systems. To study the nature of these absorbers, we have used the Gemini Multi-Object Spectrograph to conduct a deep spectroscopic galaxy redshift survey in the 5' x 5' field centered on the QSO. This survey is fully complete for r' < 19.7 and is 73% complete for r' < 21.0. We find three galaxies at the redshift of the higher z O vi system (z(abs) = 0.14232), including a galaxy at projected distance rho = 155 h(70)(-1) kpc. We find no galaxies in the Gemini field at the redshift of the lower z O vi absorber (z(abs) = 0.06807), which indicates that the nearest galaxy is more than 195 h(70)(-1) kpc away or has L < 0.04*. Previous shallower surveys covering a larger field have shown that the z(abs) = 0.06807 O vi absorber is affiliated with a group or filament of galaxies, but the nearest known galaxy has rho = 736 kpc. The z(abs) = 0.06807 absorber is notable for several reasons. The absorption profiles reveal simple kinematics indicative of quiescent material. The H I line widths and good alignment of the H I and metal lines favor photoionization, and moreover, the column density ratios imply a high metallicity: [M/H] = - 0.3 +/- 0.12. The z(abs) = 0.14232 O vi system is more complex and less constrained but also indicates a relatively high metallicity. Using galaxy redshifts from the Sloan Digital Sky Survey, we show that both of the PG 0953 + 415 O vi absorbers are located in large-scale filaments of the cosmic web. Evidently, some regions of the web filaments are highly metal enriched. We discuss the origin of the high-metallicity gas and suggest that the enrichment might have occurred long ago ( at high z).