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Constraints on the Evolution of the Ionizing Background and Ionizing Photon Mean Free Path at the End of Reionization

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arxiv 2312.08464 v1 pith:CHEHH32T submitted 2023-12-13 astro-ph.CO

classification astro-ph.CO
keywords freemeanionizingpathbackgroundreionizationalphaevolution
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abstract

The variations in Ly$\alpha$ forest opacity observed at $z>5.3$ between lines of sight to different background quasars are too strong to be caused by fluctuations in the density field alone. The leading hypothesis for the cause of this excess variance is a late, ongoing reionization process at redshifts below six. Another model proposes strong ionizing background fluctuations coupled to a short, spatially varying mean free path of ionizing photons, without explicitly invoking incomplete reionization. With recent observations suggesting a short mean free path at $z\sim6$, and a dramatic improvement in $z>5$ Ly$\alpha$ forest data quality, we revisit this latter possibility. Here we apply the likelihood-free inference technique of approximate Bayesian computation to jointly constrain the hydrogen photoionization rate $\Gamma_{\rm HI}$ and the mean free path of ionizing photons $\lambda_{\rm mfp}$ from the effective optical depth distributions at $z=5.0$-$6.1$ from XQR-30. We find that the observations are well-described by fluctuating mean free path models with average mean free paths that are consistent with the steep trend implied by independent measurements at $z\sim5$-$6$, with a concomitant rapid evolution of the photoionization rate.

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Cited by 4 Pith papers

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  1. Subaru meets JWST: A Direct Measurement of Ly$\boldsymbol{\alpha}$ Escape Fraction at $\boldsymbol{z\simeq6.2}$ with Dual Narrow-Band Imaging

    astro-ph.GA 2026-07 conditional novelty 6.5 of 10

    Completeness-weighted stacking of 56 HAEs at z≃6.2 gives median f_esc^Lyα = 0.106^{+0.066}_{-0.044} with no strong Hα-luminosity dependence and UV-linked galaxy-to-galaxy trends.

  2. An emulator for the ionizing photon mean free path in ultra-high resolution simulations: the implications of mean free path measurements for the reionization history

    astro-ph.CO 2026-02 conditional novelty 6.0 of 10

    Photon mean-free-path observations at z≈5–6, interpreted with a neural-network emulator of high-resolution radiative-transfer simulations, favor a late, extended reionization with substantial neutral hydrogen persisti...

  3. Probing the ionizing photon output of galaxies near cosmic dawn with the patchy kSZ effect

    astro-ph.CO 2025-07 conditional novelty 6.0 of 10

    In calibrated reionization simulations, the patchy kSZ power at ell~3000 correlates strongly with the start of reionization once the end is fixed by Lyman-alpha forest data, yielding model-dependent limits on early io...

  4. Reading Between the Lines: Forward Modeling Dust, Continuum, and Spectral Cleaning for Multi-Line Intensity Mapping

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    Using a SAM-based mock, multi-line intensity-mapping cross-power spectra show dust acts as a line-pair- and redshift-dependent suppression, and PCA cleaning with about 20 modes best balances line recovery against cont...

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