Inside-out or outside-in: the topology of reionization in the photon-starved regime suggested by Lyα forest data

2008/06/30 by Tirthankar Roy Choudhury, T. Roy Choudhury, Martin G. Haehnelt +3
Biochemistry, Genetics and Molecular Biology · Physics and Astronomy · #Advanced Fluorescence Microscopy Techniques #Amplitude #Astrophysics #DNA Repair Mechanisms #Dark Ages #Galaxies: Formation, Evolution, Phenomena #Galaxy #Intergalactic medium #Ionization #Lyman-alpha forest #Optics #Photon #Physics #Quantum mechanics #Reionization #Remote sensing #Spatial distribution #Spectral density #astro-ph

paper · pdf · doi:10.1111/j.1365-2966.2008.14383.x

Accepted in MNRAS. Revised for clarification, matches the accepted version

arxiv created 2008/12/17 · openalex publication_date 2009/02/13 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05

Abstract

We use a set of seminumerical simulations based on the Zel'dovich approximation, the friends-of-friends algorithm and excursion set formalism to generate reionization maps of high dynamic range with a range of assumptions regarding the distribution and luminosity of ionizing sources and the spatial distribution of sinks for the ionizing radiation. We find that ignoring the inhomogeneous spatial distribution of regions of high gas density where recombinations are important – as is often done in studies of this kind – can lead to misleading conclusions regarding the topology of reionization, especially if reionization occurs in the photon-starved regime suggested by Lyα forest data. The inhomogeneous spatial distribution of recombinations significantly reduces the mean-free path of ionizing photons and the typical size of coherently ionized regions. Reionization proceeds then much more as an outside-in process. Low-density regions far from ionizing sources become ionized before regions of high gas density not hosting sources of ionizing radiation. The spatial distribution of sinks of ionization radiation also significantly affects the shape and amplitude of the power spectrum of fluctuations of 21 cm emission. The slope of the 21 cm power spectrum as measured by upcoming 21 cm experiments should be able to distinguish to what extent the topology of reionization proceeds outside-in or inside-out, while the evolution of the amplitude of the power spectrum with increasing ionized mass fraction should be sensitive to the spatial distribution and the luminosity of ionizing sources.

Citations

• Model‐independent Insights into the Nature of the Lyα Forest and the Distribution of Matter in the Universe
• Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
• Updating reionization scenarios after recent data
• An excursion set model of hierarchical clustering: ellipsoidal collapse and the moving barrier
• Detecting the Rise and Fall of 21 cm Fluctuations with the Murchison Widefield Array
• Implications for Cosmic Reionization from the Optical Afterglow Spectrum of the Gamma-Ray Burst 050904 at z = 6.3
• The correlation between the distribution of galaxies and 21-cm emission at high redshifts
• Ultraviolet radiative feedback during the advanced stages of reionization
• The Growth of HiiRegions During Reionization
• Simulations and Analytic Calculations of Bubble Growth during Hydrogen Reionization
• Simulating cosmic reionization at large scales - I. The geometry of reionization
• Simulations of the formation, evolution and clustering of galaxies and quasars
• Three‐YearWilkinson Microwave Anisotropy Probe(WMAP) Observations: Implications for Cosmology
• Quasar H ii regions during cosmic reionization
• The observed ionization rate of the intergalactic medium and the ionizing emissivity at z >= 5: evidence for a photon-starved and extended epoch of reionization