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Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.3/55530
- A downturn in intergalactic C IV as redshift 6 is approached
- Ryan-Weber, Emma V.; Pettini, Max; Madau, Piero; Zych, Berkeley J.
- 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.
- Publication type
- Journal article
- Monthly Notices of the Royal Astronomical Society, Vol. 395, no. 3 (May 2009), pp. 1476-1490
- Publication year
- FOR Code(s)
- 0201 Astronomical and Space Sciences
- Black hole masses; CIV absorption; Cosmic star formation; Cosmology observations; Digital Sky Survey; Intergalactic medium; Luminosity functions; Ly-alpha; Quasars absorption lines; Stellar populations
- Wiley-Blackwell Publishing
- Publisher URL
- Copyright © 2009 The Authors. Journal compilation copyright © 2009 RAS.
- Peer reviewed