A Statistical Analysis of Intergalactic Medium Transmission Approaching Reionization

Abstract

We use hydrodynamic cosmological simulations in a 9.6 Mpc box to explore the evolution of the intergalactic medium (IGM) transmissivity from z=2 through the epoch of reionization. Reionization is achieved through an ultraviolet background (UVB) that includes evolving stellar and QSO source populations. We construct and analyze noiseless synthetic HI Lya absorption spectra along lines of sight through our continuously evolving box and find a smooth evolution of the effective optical depth under a power law up to the epoch of reionization. Crossing into the epoch of reionization, both the mean transmitted flux (MTF) and variance to the mean transmitted flux sharply deviate from a smooth evolution and hence such observables have large margins of error. Despite the statistical uncertainty in inferring the reionization profile from spectra, the end of an opacity phase transition of the IGM correlates well with the redshift when both the mean and variance of the transmitted flux rapidly deviate from the post-reionization profile. However, an unobtainable number of lines of sight is needed to allow an estimate of the MTF with less than 10% relative margin of error. In addition to optical transmission, we compare the predicted dark gap length distribution with observations. We show that this statistic is sensitive to spectral resolution at reionization redshifts, but overall in agreement with results by Songaila and Cowie (2002). Finally, we derive a positive correlation between the mean optical depth within a gap and the size of the gap, in attempt to relate "transmission statistics" to "dark gap statistics" in high redshift studies of the IGM.

53 pages, 24 figures

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• Four quasars above redshift 6 discovered by the Canada-France High-z Quasar Survey
• Radiative transfer simulations of cosmic reionization I: methodology and initial results
• The Evolution of Optical Depth in the Ly-alpha Forest: Evidence Against Reionization at z~6
• Inside-out or Outside-in: The topology of reionization in the photon-starved regime suggested by Lyman-alpha forest data
• The nature and evolution of the highly ionized near-zones in the absorption spectra of z~6 quasars
• Reionization and high-redshift galaxies: the view from quasar absorption lines
• The THESAN project: properties of the intergalactic medium and its connection to Reionization-era galaxies
• Glimpsing through the high redshift neutral hydrogen fog
• Long Dark Gaps in the Ly$\beta$ Forest at $z<6$: Evidence of Ultra Late Reionization from XQR-30 Spectra
• Constraining the reionization history with QSO absorption spectra
• Resolving the high redshift Lyman-alpha forest in smoothed particle hydrodynamics simulations
• Chasing the Tail of Cosmic Reionization with Dark Gap Statistics in the Ly$\alpha$ Forest over $5<z<6$
• Have We Detected Patchy Reionization in Quasar Spectra?
• Intergalactic Lyman continuum photon budget in the past 5 billion years
• Cosmic Reionization On Computers. Properties of the Post-reionization IGM
• Adaptive Mesh Refinement Simulations of the Ionization Structure and Kinematics of Damped Ly$\alpha$ Systems with Self-consistent Radiative Transfer
• The He II Post-Reionization Epoch: HST/COS Observations of the Quasar HS1700+6416
• A search for HI 21cm absorption toward the highest redshift radio loud objects
• New Evidence for Extended HeII Reionization at z>3.5 from HeII Lyman Alpha and Beta Transmission Spikes
• Quasars as probes of cosmological reionization
• Is the cosmic UV background fluctuating at redshift z ~ 6 ?
• Log-Poisson Non-Gaussianity of Ly$\alpha$ Transmitted Flux Fluctuations at High Redshift
• Subaru medium-resolution spectra of a QSO at z=6.62: Three reionization tests
• HeII Ly$\alpha$ Transmission Spikes and Absorption Troughs in Eight High-resolution Spectra Probing the End of HeII Reionization
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• Ly$\alpha$ Leaks and Reionization