You can’t see me: Super-Eddington growth hindering X-ray detection in high-z broad-line active galactic nuclei

¹ INAF, Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Italy
² Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
³ Como Lake Center for Astrophysics, DiSAT, Università degli Studi dell’Insubria, Via Valleggio 11, 22100 Como, Italy
⁴ INFN, Sezione di Milano-Bicocca, Piazza della Scienza 3, I-20126 Milano, Italy
⁵ INAF, Osservatorio Astronomico di Bologna, Via Gobetti 93/3, I-40129 Bologna, Italy
⁶ Center for Astrophysics and Space Science (CASS), New York University Abu Dhabi, PO Box 129188 Abu Dhabi, UAE
⁷ INAF, Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate, Italy
⁸ Department of Astronomy & Astrophysics, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
⁹ Dipartimento di Fisica “G. Occhialini”, Università degli Studi di Milano-Bicocca, Piazza della Scienza 3, I-20126 Milano, Italy

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Received: 20 February 2026
Accepted: 24 April 2026

Abstract

We revisit black hole mass estimates for high-redshift broad-line active galactic nuclei (AGNs) discovered with JWST by jointly analysing their broad emission lines and their systematic non-detections in deep Chandra imaging. Building upon a self-shadowed, super-Eddington accretion framework in which the corona undergoes efficient radiative over-cooling, we couple funnel-dependent Comptonisation physics with slim-disc spectral models and explore the resulting parameter space through a full Markov Chain Monte Carlo inference. Using a recently compiled sample of JWST high-redshift broad-line AGNs, we show that the observed X-ray weakness – manifested as extreme bolometric corrections, suppressed 2−10 keV luminosities, and non-detections in the 0.5−5 keV Chandra band – naturally arises when the corona is confined and radiatively over-cooled inside a narrow super-Eddington funnel. The combined broad line+X-ray analysis yields strongly bimodal posteriors: either very massive, very low-Eddington black holes (physically disfavoured), or a population of low-mass (∼10⁶ − 10⁷ M_⊙) black holes accreting at f_Edd ≫ 1. The latter solution is strongly preferred for nearly all objects and returns masses consistent with, or lower than, local M_BH − M_★ relations, mitigating the extreme mass ratios implied by single-epoch virial estimators. The predicted intrinsic spectra are redder and exhibit reduced hard-X-ray output but higher bolometric luminosities, implying bolometric corrections larger than those typical of the local AGN population, yet consistent with low-redshift highly accreting counterparts. These results support a picture in which many JWST broad-line AGNs are powered by rapidly growing, super-Eddington black holes whose suppressed coronal emission and self-shadowed broad-line region geometry combine to mimic overmassive black holes at z ≳ 6.