Delta Reion Timing

Reionization — the epoch when ultraviolet photons from the first stars and galaxies stripped the neutral hydrogen of the intergalactic medium — is constrained by multiple independent probes that do not fully agree on its timing and duration. The CMB optical depth to electron scattering measured by Planck implies reionization was largely complete by z ~ 7.7. Quasar absorption spectra show Gunn-Peterson troughs indicating substantial neutral hydrogen at z > 6, pointing to the tail end of reionization near z ~ 6. High-redshift galaxy luminosity functions and Lyman-alpha emitter statistics suggest the neutral fraction was significant at z ~ 7–8. However, the 21 cm forest and kinematic Sunyaev-Zeldovich measurements hint that reionization may have begun earlier and proceeded more patchily than a simple sudden transition model suggests. These discrepancies in the inferred timing, duration, and patchiness constitute the delta reionization timing tension.

Successive Collision Theory naturally produces an earlier onset and more extended duration of reionization than standard ΛCDM first-star models predict, resolving the timing tension without invoking exotic early universe sources. In SCT, the pre-existing stellar populations from the colliding pockets included evolved massive stars whose ultraviolet emission and supernova remnants contributed ionizing photons from the earliest post-collision epochs — well before the first generation of post-collision stars formed through standard hierarchical assembly. This pre-existing ionizing source population begins reionizing the intergalactic medium at redshifts z ~ 15–20, producing the early onset suggested by kSZ and 21 cm data. As post-collision star formation subsequently accelerates at z ~ 8–12, the combined ionizing emissivity drives reionization to completion by z ~ 6–7, consistent with the Gunn-Peterson constraint.

The patchiness of reionization in SCT reflects the angular momentum structure of the collision debris. The pre-existing ionizing sources were not uniformly distributed but concentrated along the angular momentum strata of the debris field — the same structure that produces the cosmic web of filaments and voids. Reionization therefore proceeded rapidly in overdense filamentary regions where pre-existing stars and early post-collision star formation coincided, while underdense void regions lagged behind in receiving ionizing photons. This geometry-driven patchy reionization produces a larger scatter in the neutral fraction at any given redshift than a uniform reionization model, consistent with the observed variance in Lyman-alpha emitter abundances across different lines of sight at z ~ 7.