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Title:
Tracing the re-ionization-epoch intergalactic medium with metal absorption lines
Authors:
Oppenheimer, Benjamin D.; Davé, Romeel; Finlator, Kristian
Affiliation:
AA(Astronomy Department, University of Arizona, Tucson, AZ 85721, USA; ), AB(Astronomy Department, University of Arizona, Tucson, AZ 85721, USA; ), AC(Astronomy Department, University of Arizona, Tucson, AZ 85721, USA; )
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 396, Issue 2, pp. 729-758. (MNRAS Homepage)
Publication Date:
06/2009
Origin:
MNRAS
MNRAS Keywords:
methods: numerical , galaxies: formation , galaxies: high-redshift , intergalactic medium , cosmology: theory , early Universe
DOI:
10.1111/j.1365-2966.2009.14771.x
Bibliographic Code:
2009MNRAS.396..729O

Abstract

Intergalactic medium (IGM) metal absorption lines observed in z >~ 6 spectra offer the opportunity to probe early feedback processes, the nature of enriching sources and the topology of re-ionization. We run high-resolution cosmological simulations including galactic outflows to study the observability and physical properties of five ions (CII, CIV, OI, SiII, SiIV) in absorption between z = 8 and 5. We apply three cases for ionization conditions: fully neutral, fully re-ionized and a patchy model based on the flux from the nearest galaxy. We find that our simulations can broadly fit available z ~ 5-6 IGM metal-line data, although all observations cannot be accommodated with a single ionization condition. Variations in OI absorbers among sight lines seen by Becker et al. suggest significant neutral IGM patches down to z ~ 6. Strong CIV absorbers at z ~ 6 may be the result of ionization by the galaxy responsible for that enrichment, although the identification of the neighbouring galaxy will have to wait to confirm this. Our outflows have typical speeds of ~200kms-1 and mass loading factors of ~6. Such high mass loading is critical for enriching the IGM to the observed levels while sufficiently curtailing early star formation to match the observed rest-frame ultraviolet luminosity function. The volume filling factor of metals increases during this epoch, but only reaches ~1per cent for Z > 10-3Zsolar by z = 5. Detectable absorbers generally trace inhomogeneously distributed metals residing outside of galactic haloes. CIV is an ideal tracer of IGM metals at z ~ 5-6, with dropping global ionization fractions to either higher or lower redshifts. This results in a strongly increasing global CIV mass density from z = 8 to 5, in contrast to its relative constancy from z = 5 to 2. Our simulations do not support widespread early IGM enrichment from e.g. Population III stars, as this would overpredict the numbers of weak CIV absorbers in the latest data. High-z absorbers arise from metals mostly on their first outward journey, at distances 5-50 physical kpc, and often exhibit broad profiles (δv > 200kms-1) as a result of outflowing peculiar velocities in the strongest systems. The galaxies responsible for early IGM enrichment have typical stellar masses of 107.0-8.5Msolar, and star formation rates <~1Msolaryr-1. Future facilities will be able to study the high-z galaxy-absorber connection in detail, revealing a wealth of information about feedback processes in the re-ionization epoch.
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