The Infancy of Cosmic Reionization

Abstract

We consider the early stages of cosmic hydrogen or helium reionization, when ionizing sources were still rare. We show that Poisson fluctuations in the galaxy distribution substantially affected the early bubble size distribution, although galaxy clustering was also an essential factor even at the earliest times. We find that even at high redshifts, a significant fraction of the ionized volume resided in bubbles containing multiple sources, regardless of the ionizing efficiency of sources or of the reionization redshift. In particular, for helium reionization by quasars, one-source bubbles last dominated (i.e., contained 90% of the ionized volume) at some redshift above z=7.3, and hydrogen reionization by stars achieved this milestone at z>23. For the early generations of atomic-cooling halos or molecular-hydrogen-cooling halos, one-source ionized regions dominated the ionized volume only at z>31 and z>48, respectively. To arrive at these results we develop a statistical model for the effect of density correlations and discrete sources on reionization and solve it with a Monte Carlo method.

12 pages, 8 figures, accepted by MNRAS

References in corpus (9)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
• Efficient Simulations of Early Structure Formation and Reionization
• Radiative transfer simulations of cosmic reionization I: methodology and initial results
• The Physics and Early History of the Intergalactic Medium
• The History and Morphology of Helium Reionization
• The Difference PDF of 21-cm Fluctuations: A Powerful Statistical Tool for Probing Cosmic Reionization
• Detecting Early Galaxies Through Their 21-cm Signature
• On Correlated Random Walks and 21-cm Fluctuations During Cosmic Reionization