The Detection of Oxygen in the Low-Density Intergalactic Medium
Abstract
The abundances of metals in the intergalactic medium (IGM) can be used to constrain the amount of star formation at high redshift and the spectral shape of the ionizing background radiation. For both purposes, it is essential to measure the abundances in regions of low density, away from local sources of metals and ionizing photons. Here we report the first detection of O VI in the low-density IGM at high redshift. We perform a pixel-by-pixel search for O VI absorption in eight high-quality quasar spectra spanning the redshift range z=2.0-4.5. At 2<~z<~3, we clearly detect O VI in the form of a positive correlation between the H I Lyα optical depth and the optical depth in the corresponding O VI pixel, down to τHI~10-1. This is an order of magnitude lower in τHI than the best C IV measurements can probe, and it constitutes the first clear detection of metals in underdense gas. The nondetection of O VI at z>3 is consistent with the enhanced photoionization from a hardening of the UV background below z~3 but could also be caused by the high level of contamination from Lyman series lines. Part of the data presented herein was obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The W. M. Keck Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2000
- DOI:
- 10.1086/312892
- arXiv:
- arXiv:astro-ph/0008011
- Bibcode:
- 2000ApJ...541L...1S
- Keywords:
-
- Cosmology: Observations;
- Galaxies: Formation;
- Galaxies: Intergalactic Medium;
- Galaxies: Quasars: Absorption Lines;
- Astrophysics
- E-Print:
- 5 pages, 2 figures. Reference added to match published version