2009/02/19 by Emma V. Ryan-Weber, Emma Ryan‐Weber, Max Pettini +2
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #Radio Astronomy Observations and Technology #astro-ph.CO
paper · pdf · doi:10.1111/j.1365-2966.2009.14618.x
15 pages, 8 Figures, Accepted for publication in Monthly Notices of the Royal Astronomical Society. Typo in astro-ph abstract fixed. Paper unchanged
arxiv created 2009/02/19 · openalex publication_date 2009/04/23 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We present the results of the largest survey to date for intergalactic metals at redshifts z > 5, using near-IR spectra of nine quasi-stellar objects with emission redshifts zem > 5.7. We detect three strong C iv doublets at zabs= 5.7–5.8, two low-ionization systems at zabs > 5 and numerous Mg ii absorbers at zabs= 2.5–2.8. We find, for the first time, a change in the comoving mass density of C iv ions as we look back to redshifts z > 5. At a mean 〈z〉= 5.76, we deduce ΩC iv= (4.4 ± 2.6) × 10−9 which implies a drop by a factor of ∼3.5 compared to the value at z < 4.7, after accounting for the differing sensitivities of different surveys. The observed number of C iv doublets is also lower by a similar factor, compared to expectations for a non-evolving column density distribution of absorbers. These results point to a rapid build-up of intergalactic C iv over a period of only ∼300 Myr; such a build-up could reflect the accumulation of metals associated with the rising levels of star formation activity from z∼ 9 indicated by galaxy counts, and/or an increasing degree of ionization of the intergalactic medium (IGM), following the overlap of ionization fronts from star-forming regions. If the value of ΩC iv we derive is typical of the IGM at large, it would imply a metallicity ZIGM≳ 10−4 Z⊙. The early-type stars responsible for synthesizing these metals would have emitted only about one Lyman continuum photon per baryon prior to z= 5.8; such a background is insufficient to keep the IGM ionized and we speculate on possible factors which could make up the required shortfall.