A new analytical formalism self-consistently predicts both the ionized fraction x_i(z) and photoionization rate Gamma_HI(z), achieving percent-level accuracy in x_i and 20-30% accuracy in Gamma_HI versus radiative transfer simulations at z less than or equal to 6.
Large Fluctuations in the High-Redshift Metagalactic Ionizing Background
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abstract
Recent observations have shown that the scatter in opacities among coeval segments of the Lyman-alpha forest increases rapidly at z > 5. In this paper, we assess whether the large scatter can be explained by fluctuations in the ionizing background in the post-reionization intergalactic medium. We find that matching the observed scatter at z ~ 5.5 requires a short spatially averaged mean free path of < 15 comoving Mpc/h, a factor of > 3 shorter than direct measurements at z ~ 5.2. We argue that such rapid evolution in the mean free path is difficult to reconcile with our measurements of the global H I photoionization rate, which stay approximately constant over the interval z ~ 4.8 - 5.5. However, we also show that measurements of the mean free path at z > 5 are likely biased towards higher values by the quasar proximity effect. This bias can reconcile the short values of the mean free path that are required to explain the large scatter in opacities. We discuss the implications of this scenario for cosmological reionization. Finally, we investigate whether other statistics applied to the z > 5 Lyman-alpha forest can shed light on the origin of the scatter. Compared to a model with a uniform ionizing background, models that successfully account for the scatter lead to enhanced power in the line-of-sight flux power spectrum on scales k < 0.1 h/Mpc. We find tentative evidence for this enhancement in observations of the high-redshift Lyman-alpha forest.
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Long gamma-ray bursts imply a higher cosmic star formation rate density at z>6 than galaxy surveys detect, sufficient to drive reionization with moderate ionizing efficiency and escape fraction, implying a large population of undetected faint galaxies.
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A self-consistent analytical model for both the photoionization rate and reionization history
A new analytical formalism self-consistently predicts both the ionized fraction x_i(z) and photoionization rate Gamma_HI(z), achieving percent-level accuracy in x_i and 20-30% accuracy in Gamma_HI versus radiative transfer simulations at z less than or equal to 6.
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Gamma-ray bursts reveal the history and faint contributors of cosmic reionization
Long gamma-ray bursts imply a higher cosmic star formation rate density at z>6 than galaxy surveys detect, sufficient to drive reionization with moderate ionizing efficiency and escape fraction, implying a large population of undetected faint galaxies.