The spectrum of the low-redshift QSO PG 0953+415 (zQSO=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'×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 (zabs=0.14232), including a galaxy at projected distance ρ=155 h-170 kpc. We find no galaxies in the Gemini field at the redshift of the lower z O VI absorber (zabs=0.06807), which indicates that the nearest galaxy is more than 195 h-170 kpc away or has L<0.04L*. Previous shallower surveys covering a larger field have shown that the zabs=0.06807 O VI absorber is affiliated with a group or filament of galaxies, but the nearest known galaxy has ρ=736 h-170 kpc. The zabs=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 zabs=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).Based on observations with (1) the NASA/ESA Hubble Space Telescope (HST), obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555 (2) the NASA-CNES-ESA Far Ultraviolet Spectroscopic Explorer (FUSE), operated for NASA by Johns Hopkins University under NASA contract NAS 5-32985 and (3) the Gemini Observatory, which is operated by AURA, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (US), the Particle Physics and Astronomy Research Council (UK), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil), and CONICET (Argentina).
The Astrophysical Journal
- Pub Date:
- June 2006
- Galaxies: Intergalactic Medium;
- Galaxies: Quasars: Absorption Lines;
- Galaxies: Quasars: Individual: Alphanumeric: PG 0953+415;
- Submitted for publication in the Astrophysical Journal Letters. Figs. 1 and 2 compressed for astro-ph. High-resolution version available at http://www.astro.umass.edu/~tripp/astro/qualitypreps/pg0953tripp.pdf