The abundance and physical properties of O VII and O VIII X-ray absorption systems in the EAGLE simulations

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 $N_{\mathrm{H}\mathrm{I}}\gtrsim 10^{15}{\mathrm{cm}}^{-2}$, 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.

Accepted for publication in MNRAS. Minor changes w.r.t version 1 including updated values for Table 2

References in corpus (9)

• The EAGLE project: Simulating the evolution and assembly of galaxies and their environments
• The EAGLE simulations of galaxy formation: calibration of subgrid physics and model variations
• The Circumgalactic Medium
• The effect of photo-ionization on the cooling rates of enriched, astrophysical plasmas
• Chemical enrichment in cosmological, smoothed particle hydrodynamics simulations
• The Search for the Missing Baryons at Low Redshift
• The Athena X-ray Integral Field Unit (X-IFU)
• Absorption signatures of warm-hot gas at low redshift: OVI
• Detection of the Missing Baryons toward the Sightline of H1821+643

Cited by in corpus (13)

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• The metal content of the hot atmospheres of galaxy groups
• The Physical Origins of the Identified and Still Missing Components of the Warm-Hot Intergalactic Medium: Insights from Deep Surveys in the Field of Blazar 1ES1553+113
• Hot WHIM counterparts of FUV OVI absorbers: Evidence in the line-of-sight towards quasar 3C 273
• Clumpiness of Observed and Simulated Cold Circumgalactic Gas
• Prospects of detecting soft X-ray emission from typical WHIM filaments around massive clusters and the Coma cluster soft excess
• Detection capabilities of the Athena X-IFU for the warm-hot intergalactic medium using gamma-ray burst X-ray afterglows
• Cosmic metal invaders: Intergalactic OVII as a tracer of the warm-hot intergalactic medium within cosmic filaments in the EAGLE simulation
• A WHIM origin for the soft excess emission in the Coma cluster
• Galaxy cluster photons alter the ionisation state of the nearby warm-hot intergalactic medium