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arXiv · 2609.28257

JWST evidence for a sharp "Cosmic Daybreak" at z = 15

Jiashuo Zhang·Tom Broadhurst·Tzihong Chiueh·Keiichi Umetsu·Hsi-Yu Schive·Chian-Chou Chen·Jeremy Lim·Jose M. Diego·Paloma Morilla·Pablo G. Perez-Gonzalez·Rogier Windhorst
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Abstract

Luminous young galaxies have been uncovered with relative ease by JWST, extending to z=14.5, so it is puzzling that deeper spectroscopy of fainter candidates now finds only interlopers. This redshift `ìmpasse" is underscored by the measured stellar ages of these high-z galaxies, which we show converge to zero by z=15, with a marked absence of earlier star-formation. Taken literally, such a late transition from the Dark Ages to luminous galaxies is unlike the gradual Cosmic Dawn of standard LCDM, but does confirm a key prediction of Wave Dark Matter, $ψ$DM, as a Bose-Einstein condensate. The de Broglie wave pressure resists gravity until a substantial Jeans mass of $4\times 10^9M_\odot$ is overcome at z$=$15, corresponding to a light boson $m_ψ=2.2_{-0.3}^{+0.4} \times 10^{-22}$eV, and similar to independent estimates from lensing anomalies and dwarf galaxies. Furthermore, the substantial luminosities of the highest redshift galaxies appear to converge to the initial Jeans scale of $ψ$DM, whereas LCDM predictions extend to lower luminosities and larger ages than observed. These contrasting predictions can be definitively tested as JWST observations accumulate, with diametric implications for Dark Matter as heavy particles beyond the Standard Model, or ultra-light bosons motivated by the String Axiverse.

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Jiashuo Zhang, Tom Broadhurst, Tzihong Chiueh, Keiichi Umetsu, Hsi-Yu Schive, Chian-Chou Chen, Jeremy Lim, Jose M. Diego, Paloma Morilla, Pablo G. Perez-Gonzalez, Rogier Windhorst. 2026-09-23. JWST evidence for a sharp "Cosmic Daybreak" at z = 15. https://arxiv.org/abs/2609.28257

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