Fig. 1.

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Reionization history in ΛCDM based on new JWST observations of structure formation in the early Universe. Lower panel: the neutral fraction xHI as a function of redshift z, for a cutoff MUV = −14.6 and a JWST-calibrated ionizing efficiency, ξion, and escape fraction (fesc) inferred from low-z analogues. The blue data points represent measured observational constraints (see text for references). Upper panel: CMB optical depth, τCMB, as a function of z. The blue band represents the Planck measurement and its uncertainty (Planck Collaboration VI 2020). The for the xHI fit is 4.36, and τCMB differs from the Planck optimized value by ∼2σ. The new JWST galaxy observations thus create significant tension for the standard model, both for the reionization history and the CMB optical depth.
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