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Observations of metals in the z approximate to 3.5 intergalactic medium and comparison to the EAGLE simulations

Turner, ML and Schaye, J and Crain, RA and Theuns, T and Wendt, M (2016) Observations of metals in the z approximate to 3.5 intergalactic medium and comparison to the EAGLE simulations. Monthly Notices of the Royal Astronomical Society, 462 (3). pp. 2440-2464. ISSN 0035-8711

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Abstract

We study the z ≈ 3.5 intergalactic medium (IGM) by comparing new, high-quality absorption spectra of eight QSOs with _zQSO_ = 3.75, to virtual observations of the Evolution and Assembly of Galaxies and their Environments (EAGLE) cosmological hydrodynamical simulations. We employ the pixel optical depth method and uncover strong correlations between various combinations of HI, CIII, CIV, Si III, Si IV, and OVI.We find good agreement between many of the simulated and observed correlations, including τOVI(τHI). However, the observed median optical depths for the τCIV(τHI) and τSi IV(τHI) relations are higher than those measured from the mock spectra. The discrepancy increases from up to ≈0.1 dex at τHI = 1 to ≈1 dex at τHI = 102, where we are likely probing dense regions at small galactocentric distances. As possible solutions, we invoke (a) models of ionizing radiation softened above 4 Ryd to account for delayed completion of He II reionization; (b) simulations run at higher resolution; (c) the inclusion of additional line broadening due to unresolved turbulence; and (d) increased elemental abundances; however, none of these factors can fully explain the observed differences.
Enhanced photoionization of HI by local sources, which was not modelled, could offer a solution. However, the much better agreement with the observed OVI(H I) relation, which we find probes a hot and likely collisionally ionized gas phase, indicates that the simulations are not in tension with the hot phase of the IGM, and suggests that the simulated outflows may entrain insufficient cool gas.

Item Type: Article
Additional Information: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record Monica L. Turner, Joop Schaye, Robert A. Crain, Tom Theuns, and Martin Wendt Observations of metals in the z ≈ 3.5 intergalactic medium and comparison to the EAGLE simulations MNRAS (November 01, 2016) Vol. 462 2440-2464 doi:10.1093/mnras/stw1816 first published online July 28, 2016 is available online at: http://dx.doi.org/10.1093/mnras/stw1816
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Related URLs:
Date Deposited: 01 Nov 2016 09:34
Last Modified: 01 Nov 2016 09:34
DOI or Identification number: 10.1093/mnras/stw1816
URI: http://researchonline.ljmu.ac.uk/id/eprint/4710

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