Assuming Ionization Equilibrium and the Impact on the Lyman-$\alpha$ Forest Power Spectrum during the End of Reionization at $8\ge z\ge 5$

Abstract

We explore how the assumption of ionization equilibrium modulates the modeled intergalactic medium (IGM) at the end of the hydrogen Epoch of Reionization using the cosmological radiation hydrodynamic \textsc{Technicolor Dawn} simulation. In neutral and partially-ionized regions where the metagalactic ultraviolet background (UVB) is weak, the ionization timescale $t_{\mathrm{ion}}\equiv {\Gamma }^{-1}$ exceeds the Hubble time. Assuming photoionization equilibrium in such regions artificially boosts the ionization rate, accelerating reionization. By contrast, the recombination time $t_{\mathrm{rec}}<t_{\mathrm{ion}}$ in photoionized regions, with the result that assuming photoionization equilibrium artificially increases the neutral hydrogen fraction. Using snapshots between $8\ge z\ge 5$, we compare the predicted Lyman-$\alpha$ forest flux power spectrum with and without the assumption of ionization equilibrium. Small scales ($k>0.1$ rad s km${}^{-1}$) exhibit reduced power from $7\le z\le 5.5$ in the ionization equilibrium case while larger scales are unaffected. This occurs for the same reasons: ionization equilibrium artificially suppresses the neutral fraction in self-shielded gas and boosts ionizations in voids, suppressing small-scale fluctuations in the ionization field. When the volume-averaged neutral fraction drops below $10^{-4}$, the signature of non-equilibrium ionizations on the Lyman-$\alpha$ forest (LAF) disappears. Comparing with recent observations indicates that these non-equilibrium effects are not yet observable in the LAF flux power spectrum.

arXiv commentThis has been submitted and accepted to ApJ as of April 11, 2022

References in corpus (37)

• Array Programming with NumPy
• The cosmological simulation code GADGET-2
• Cosmological SPH simulations: A hybrid multi-phase model for star formation
• Constraining the Evolution of the Ionizing Background and the Epoch of Reionization with z ~ 6 Quasars II: A Sample of 19 Quasars
• Cosmological Simulations with TreeSPH
• Gusty, gaseous flows of FIRE: galactic winds in cosmological simulations with explicit stellar feedback
• Hydrodynamic Simulations of Galaxy Formation. II. Photoionization and the Formation of Low Mass Galaxies
• Reionization after Planck: The Derived Growth of the Cosmic Ionizing Emissivity now matches the Growth of the Galaxy UV Luminosity Density
• A General Class of Lagrangian Smoothed Particle Hydrodynamics Methods and Implications for Fluid Mixing Problems
• Evidence of patchy hydrogen reionization from an extreme Ly$\alpha$ trough below redshift six
• New Determinations of the UV Luminosity Functions from z~9 to z~2 show a remarkable consistency with halo growth and a constant star formation efficiency
• P3M-SPH simulations of the Lyman-alpha Forest
• The Evolution of the Intergalactic Medium
• Conditions for Reionizing the Universe with A Low Galaxy Ionizing Photon Escape Fraction
• Model-independent insights into the nature of the Lyman-alpha forest and the distribution of matter in the universe
• The spectral evolution of the first galaxies. I. James Webb Space Telescope detection limits and color criteria for population III galaxies
• The Lyman-$\alpha$ forest in optically-thin hydrodynamical simulations
• Long troughs in the Lyman-$\alpha$ forest below redshift 6 due to islands of neutral hydrogen
• Radiative Transfer Effects during Photoheating of the Intergalactic Medium
• Revealing reionization with the thermal history of the intergalactic medium: new constraints from the Lyman-$\alpha$ flux power spectrum
• Reionization and galaxy inference from the high-redshift Lyα forest
• Quasar Proximity Zones and Patchy Reionization
• Self-Consistent Modeling of Reionization in Cosmological Hydrodynamical Simulations
• Cosmic distribution of highly ionized metals and their physical conditions in the EAGLE simulations
• Flickering AGN can explain the strong circumgalactic O VI observed by COS-Halos
• The impact of feedback from galaxy formation on the Lyman-alpha transmitted flux
• Reionization in Technicolor
• Heating of the Intergalactic Medium by Hydrogen Reionization
• Pressure Support vs. Thermal Broadening in the Lyman-alpha Forest I: Effects of the Equation of State on Longitudinal Structure
• An Introductory Review on Cosmic Reionization
• Inferring the IGM thermal history during reionisation with the Lyman-$\alpha$ forest power spectrum at redshift $z\simeq 5$
• The Late Reionization of Filaments
• Imprints of temperature fluctuations on the $z\sim 5$ Lyman-$\alpha$ forest: a view from radiation-hydrodynamic simulations of reionization
• The impact of AGN feedback on the 1D power spectra from the Ly$\alpha$ forest using the Horizon-AGN suite of simulations
• The Faint Host Galaxies of C IV Absorbers at z > 5
• Effect of non-equilibrium ionization on derived physical conditions of the high-$z$ intergalactic medium
• Photoevaporation of Minihalos during Cosmic Reionization: Primordial and Metal-Enriched Halos

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• The Sherwood-Relics simulations: overview and impact of patchy reionization and pressure smoothing on the intergalactic medium
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