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Abstract Recent JWST observations atz > 6 may imply galactic ionizing photon production above prior expectations. Under observationally motivated assumptions about escape fractions, these suggest az ~ 8–9 end to reionization, in tension with thez < 6 end required by the Lyαforest. In this work, we use radiative transfer simulations to understand what different observations tell us about when reionization ended and when it started. We consider a model that ends too early (zend ≈ 8) alongside two more realistic scenarios withzend ≈ 5: one starting late (z ~ 9) and another early (z ~ 13). We find that the latter requires up to an order-of-magnitude evolution in galaxy ionizing properties at 6 < z < 12, perhaps in tension with measurements ofξionby JWST, which indicate little evolution. We study how these models compare to recent measurements of the Lyαforest opacity, mean free path, intergalactic medium thermal history, visibility ofz > 8 Lyαemitters, and the patchy kSZ signal from the cosmic microwave background (CMB). We find that neither of the late-ending scenarios is strongly disfavored by any single data set. However, a majority of observables, spanning several distinct types of observations, prefer a late start. Not all probes agree with this conclusion, hinting at a possible lack of concordance arising from deficiencies in observations and/or theoretical modeling. Observations by multiple experiments (including JWST, Roman, and CMB-S4) in the coming years will establish a concordance picture of reionization's beginning or uncover such deficiencies.
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Constraints on the Evolution of the Ionizing Background and Ionizing Photon Mean Free Path at the End of Reionization
Abstract The variations in Lyαforest opacity observed atz> 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 atz∼ 6, and a dramatic improvement inz> 5 Lyαforest data quality, we revisit this latter possibility. Here, we apply the likelihood-free inference technique of approximate Bayesian computation (ABC) to jointly constrain the hydrogen photoionization rate ΓHIand the mean free path of ionizing photonsλmfpfrom the effective optical depth distributions atz= 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 atz∼ 5–6, with a concomitant rapid evolution of the photoionization rate.
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- PAR ID:
- 10520627
- Publisher / Repository:
- IOP
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 965
- Issue:
- 2
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 134
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/1538-4357/ad1d5d
