You can't see me: super-Eddington growth hindering X-ray detection in high-z broad-line AGNs

Alessandro Trinca, Alessandro Lupi, Francesco Haardt, Piero Madau

First listed 2026-02-25 | Last updated 2026-02-25

Abstract

We revisit black hole mass estimates for high-redshift broad-line AGNs discovered with JWST by jointly analysing their broad emission lines and their systematic non-detections in deep Chandra imaging. Building upon the self-shadowed, super-Eddington accretion flow framework and the coronal over-cooling prescription of Madau & Haardt (2024), we couple funnel-dependent Comptonization physics with slim-disc spectra from Kubota & Done (2019) and explore the resulting parameter space through a full MCMC inference. Using the sample analysed by Lupi et al. (2024) and Maiolino et al. (2025), we show that 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 ($\sim 10^{6}-10^{7} ~M_{\odot}$) black holes accreting at $f_{\rm Edd} \gg 1$. The latter solution is strongly preferred for nearly all objects and returns masses consistent with, or lower than, local $M_{\rm BH}-M_{\rm star}$ 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 BLR geometry combine to mimic overmassive black holes at $z \gtrsim 6$.

Short digest

Jointly modeling broad-line widths with deep Chandra non-detections, this work reinterprets JWST-selected high-z broad-line AGNs using a self-shadowed, super-Eddington funnel plus slim-disc Comptonization framework in a full MCMC. Applied to 14 sources from Lupi (2024b) and Maiolino (2025), the X-ray weakness—extreme bolometric corrections, suppressed 2–10 keV, and 0.5–5 keV non-detections—emerges naturally when the corona is confined and radiatively over-cooled inside a narrow funnel. The posteriors are strongly bimodal but favor low-mass (~10^6–10^7 Msun), highly super-Eddington solutions over very massive, low-Eddington ones, yielding masses consistent with or below local MBH–Mstar. Predicted SEDs are redder with reduced hard-X-ray output and larger bolometric corrections, arguing that many high-z broad-line AGNs are rapidly growing super-Eddington black holes rather than overmassive outliers.

Key figures to inspect

• Fig. 1 (kTe and Γ vs funnel half-opening angle): shows how narrowing the super-Eddington funnel steepens the X-ray slope and cools the corona—the key lever producing X-ray weakness.
• Predicted L2–10 keV and observed-frame 0.5–5 keV versus Chandra limits for the 14 objects: verify that model luminosities/fluxes fall below the upper limits and how this varies with redshift and funnel angle.
• Corner/posterior plots for representative sources: inspect the bimodality (high-M/low-fEdd vs low-M/high-fEdd) and how adding X-ray non-detections to broad-line constraints drives the preference for super-Eddington, low-mass BHs.
• MBH versus Mstar comparison: check that re-inferred masses align with or fall below the local MBH–Mstar relation, mitigating extreme BH/host ratios from single-epoch virials.
• Grid of intrinsic SEDs from the agnslim library with funnel-dependent Comptonization: see the redder continua, reduced hard-X-ray output, and the implied large bolometric corrections relative to local AGN templates.