Chasing the beginning of reionization in the JWST era
Abstract
Recent JWST observations at $z > 6$ may imply galactic ionizing photon production in excess of prior expectations. Under observationally motivated assumptions about escape fractions, these suggest a $z \sim 8-9$ end to reionization, in strong tension with the $z < 6$ end required by the Ly$\alpha$ forest. 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 (at $z \approx 8$) alongside two more realistic scenarios that end late at $z \approx 5$: one that starts late ($z \sim 9$) and another that starts early ($z \sim 13$). 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 recent measurements of $\xi_{\rm ion}$ by JWST, which indicate little evolution. We also study how these models compare to recent measurements of the Ly$\alpha$ forest opacity, mean free path, IGM thermal history, visibility of $z > 8$ Ly$\alpha$ emitters, and the patchy kSZ signal from the CMB. We find that neither of the late-ending scenarios is conclusively disfavored by any single data set. However, a majority of these 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 between observables. Observations by multiple experiments (including JWST, Roman, and CMB-S4) in the coming years will either establish a concordance picture of reionization's early stages or reveal systematics in data and/or theoretical modeling.
- Publication:
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arXiv e-prints
- Pub Date:
- September 2024
- DOI:
- 10.48550/arXiv.2409.02989
- arXiv:
- arXiv:2409.02989
- Bibcode:
- 2024arXiv240902989C
- Keywords:
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- Astrophysics - Cosmology and Nongalactic Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 21+7 pages, 13+2 figures, submitted to ApJ. Comments welcome