A selection-aware evidence horizon for early cosmic chemical enrichment

Abstract

Record-redshift metal detections are compelling but statistically unstable markers of early chemical enrichment. We define a chemical-evidence horizon as the selection-conditioned probability of recording an unambiguous metal line. In JADES DR4, 524 robust z ≥ 5 galaxies give z50 = 10.66 (95% bootstrap 9.91–11.88) at MUV = −20 and 30 ks; a photometric-target denominator gives 12.52 (11.10–16.44). Repeated subsampling shifts the median maximum redshift from 8.37 at n = 10 to 11.28 at n = 400. Target-level catalogue-noise injection–recovery shows that [O III] 5007 egress at z = 9.59–9.98 and the subsequent reliance on weaker line families generate a bandpass-driven evidence envelope. ALPINE [C II] data independently calibrate a +211 km s−1 median Lyα systemic offset, and published 21-cm results remain upper limits. The framework replaces a pioneer-object chronology with a reproducible observational distribution and defines the common-field forward model needed to infer a physical enrichment boundary.