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Wijers, NA, Schaye, J, Oppenheimer, BD, Crain, RA and Nicastro, F (2019) The abundance and physical properties of O VII and O VIII X-ray absorption systems in the EAGLE simulations. Monthly Notices of the Royal Astronomical Society, 488 (2). p. 2947. ISSN 0035-8711
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Abstract
We use the EAGLE cosmological, hydrodynamical simulations to predict the column density and equivalent width distributions of intergalactic O VII ($E=574$ eV) and O VIII ($E=654$ eV) absorbers at low redshift. These two ions are predicted to account for 40% of the gas-phase oxygen, which implies that they are key tracers of cosmic metals. We find that their column density distributions evolve little at observable column densities from redshift 1 to 0, and that they are sensitive to AGN feedback, which strongly reduces the number of strong (column density $N \gtrsim 10^{16} \, \mathrm{cm}^{-2})$ absorbers. The distributions have a break at $N \sim 10^{16} \, \mathrm{cm}^{-2}$, corresponding to overdensities of $\sim 10^{2}$, likely caused by the transition from sheet/filament to halo gas. Absorption systems with $N \gtrsim 10^{16} \mathrm{cm}^{-2}$ are dominated by collisionally ionized O VII and O VIII, while the ionization state of oxygen at lower column densities is also influenced by photoionization. At these high column densities, O VII and O VIII arising in the same structures probe systematically different gas temperatures, meaning their line ratio does not translate into a simple estimate of temperature. While O VII and O VIII column densities and covering fractions correlate poorly with the H I column density at $N_{\mathrm{H \, I}} \gtrsim 10^{15} \, \mathrm{cm}^{-2}$, O VII and O VIII column densities are higher in this regime than at the more common, lower H I column densities. The column densities of O VI and especially Ne VIII, which have strong absorption lines in the UV, are good predictors of the strengths of O VII and O VIII absorption and can hence aid in the detection of the X-ray lines.
| Item Type: | Article |
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| Additional Information: | This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2019 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. |
| 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: | 10 Sep 2019 10:04 |
| Last Modified: | 04 Sep 2021 09:01 |
| DOI or ID number: | 10.1093/mnras/stz1762 |
| URI: | https://researchonline.ljmu.ac.uk/id/eprint/11178 |
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