2005/11/17 by George D. Becker, W. L. W. Sargent, Wallace L. W. Sargent +2 · 1 citation
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #Gamma-ray bursts and supernovae #astro-ph
paper · pdf · doi:10.1086/500079
published as Astrophys.J.640:69-80,2006 · Submitted to ApJ, with changes to reflect referee's comments
arxiv created 2005/11/17 · openalex publication_date 2006/03/13 · arxiv updated 2009/12/01 · openalex created_date 2022/10/06 · openalex updated_date 2026/07/31
We present a search for O I in the spectra of nine 4.9 ≤ z QSO ≤ 6.4 QSOs taken with Keck HIRES. We detect six systems with N > 10 13.7 cm -2 in the redshift intervals where O I λ1302 falls redward of the Lyα forest. Four of these lie toward SDSS J1148+5251 ( z QSO = 6.42). This imbalance is unlikely to arise from variations in sensitivity among our data or from a statistical fluctuation. The excess O I occurs over a redshift interval that also contains transmission in Lyα and Lyβ. Therefore, if these O I systems represent pockets of neutral gas, then they must occur within or near regions of the IGM that are highly ionized. In contrast, no O I is detected toward SDSS J1030+0524 ( z QSO = 6.30), whose spectrum shows complete absorption in Lyα and Lyβ over Δ z ~ 0.2. Assuming no ionization corrections, we measure mean abundance ratios ⟨[O/Si]⟩ = -0.04 ± 0.06, ⟨[C/O]⟩ = -0.31 ± 0.09, and ⟨[C/Si]⟩ = -0.34 ± 0.07 (2 σ), which are consistent with enrichment dominated by Type II supernovae. The O/Si ratio limits the fraction of silicon in these systems contributed by metal-free very massive stars to ≲30%, a result that is insensitive to ionization corrections. The ionic comoving mass densities along the z QSO > 6.2 sight lines, including only the detected systems, are Ω = (7.0 ± 0.6) × 10 -8 , Ω = (9.6 ± 0.9) × 10 -9 , and Ω = (1.5 ± 0.2) × 10 -8 .