Improved treatments of the ionizing photon mean free path in semi-numerical simulations of reionization

Abstract

Efficient and accurate simulations of the reionization epoch are crucial to exploring the vast uncharted parameter space that will soon be constrained by measurements of the 21 cm power spectrum. One of these parameters, $R_{\max }$, is meant to characterize the absorption of photons by residual neutral gas inside of ionized regions, but has historically been implemented in a very simplistic fashion acting only as a maximum filtering scale. We leverage the correspondence between excursion set methods and the integrated flux from ionizing sources to define two physically-motivated prescriptions of the mean free path of ionizing photons that smoothly attenuate the contribution from distant sources. Implementation of these methods in semi-numerical reionization codes requires only modest additional computational effort due to the fact that spatial filtering is still performed on scales larger than the characteristic absorption distance. We find that our smoothly-defined mean free path prescriptions more effectively suppress large-scale structures in the ionization field in semi-numerical reionization simulations compared to the standard $R_{\max }$ approach, and the magnitude of the mean free path modulates the power spectrum in a much smoother manner. We show that this suppression of large-scale power is significant enough to be relevant for upcoming 21 cm power spectrum observations. Finally, we show that in our model the mean free path plays a larger role in regulating the reionization history than in models using $R_{\max }$.

13 pages, 12+2 figures, accepted for publication in MNRAS

References in corpus (15)

• Efficient Simulations of Early Structure Formation and Reionization
• The morphology of HII regions during reionization
• Improved upper limits on the 21-cm signal power spectrum of neutral hydrogen at $\mathbf{z}\approx 9.1$ from LOFAR
• 21CMMC: an MCMC analysis tool enabling astrophysical parameter studies of the cosmic 21 cm signal
• Deep multi-redshift limits on Epoch of Reionisation 21cm Power Spectra from Four Seasons of Murchison Widefield Array Observations
• Inside-out or Outside-in: The topology of reionization in the photon-starved regime suggested by Lyman-alpha forest data
• Cosmic Reionization On Computers I. Design and Calibration of Simulations
• The mean free path of ionizing photons at 5 < z < 6: evidence for rapid evolution near reionization
• The THESAN project: properties of the intergalactic medium and its connection to Reionization-era galaxies
• Fast Large-Scale Reionization Simulations
• A short mean free path at $z=6$ favors late and rapid reionization by faint galaxies
• The Predicament of Absorption-Dominated Reionization: Increased Demands on Ionizing Sources
• AMBER: A Semi-numerical Abundance Matching Box for the Epoch of Reionization
• Bayesian Model Selection with Future 21cm Observations of The Epoch of Reionisation
• Effects of Small-Scale Absorption Systems on Neutral Islands during the Late Epoch of Reionization

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• LIMFAST. I. A Semi-Numerical Tool for Line Intensity Mapping
• Probing Population III Initial Mass Functions with He II/H$\alpha$ Intensity Mapping
• The importance of stochasticity in determining galaxy emissivities and UV LFs during cosmic dawn and reionization
• The large-scale 21-cm power spectrum from reionization
• Efficient exploration of reionization parameters for the upcoming 21 cm observations using a photon conserving semi-numerical model SCRIPT
• Efficient simulation of discrete galaxy populations and associated radiation fields during the first billion years
• Effects of chemically homogeneous evolution of the first stars on the 21-cm signal and reionization
• Efficient Modelling of Lyman-α opacity fluctuations during late reionization epoch
• A local, topology-independent parameterization of quasar IGM damping wings
• First constraints on the local ionization topology in front of two quasars at z ~ 7.5