The X-ray weakness of Little Red Dots and JWST-selected AGN: comparison with local AGN in different accretion regimes

A. Tortosa, C. Ricci, P. Du, G. Venturi, L. C. Ho, R. Li, J. -M. Wang, M. Berton

First listed 2026-03-10 | Last updated 2026-03-14

Abstract

We investigate the origin of the observed X-ray weakness in high z LRDs and other JWST-selected broad line AGN by comparing their X-ray and optical properties with those of a diverse sample of low z AGN, including super-Eddington accreting massive black holes (SEAMBHs), NLS1s, and type I AGN from large surveys. We examine the relations between X-ray luminosity, broad Hα line luminosity, Eddington ratio, bolometric luminosity and X-ray-to-bolometric luminosity correction, and explore whether high z sources may represent analogues of local highly accreting systems. While a few LRDs and JWST-selected AGN are consistent with the SEAMBHs population in the $L_x/L_{Hα}$ versus $λ_{Edd}$ plane, most lie below it, suggesting either more extreme accretion conditions, suppressed coronal emission or heavy obscuration. We identify an anti-correlation between $L_x/L_{Hα}$ and $λ_{Edd}$ in the low z, high accreting subsample, consistent with theoretical expectations of slim-disc accretion. We further show that, for SEAMBHs, $Hα$-based bolometric luminosities underestimate SED-based values even after dust correction. We find that SEAMBHs, LRDs, and JWST-selected AGN occupy a similar high-$κ_{bol,x}$ regime, indicating that the relative deficit of X-ray emission compared to the bolometric output could potentially support the view that soft X-ray spectra arising from relatively cold coronae is a common feature of highly accreting systems across cosmic time. Our results are consistent with the idea that the observed X-ray weakness of LRDs and JWST-selected AGN may be linked to the physics of highly accreting SMBHs. Moreover, observational limitations at high z, including instrumental sensitivity and the steep X-ray spectra expected for highly accreting systems, likely further suppress the detected X-ray signal.

Short digest

Compares z≳4 little red dots and JWST-selected broad-line AGN to local SEAMBHs, NLS1s, and type I AGN using L2–10 keV, broad Hα, λEdd, Lbol, and κbol,X. Finds an anti-correlation between L2–10 keV/LHα and λEdd in the local high-λEdd subsample (slim-disc–like), while most high‑z objects fall below the SEAMBH locus, implying more extreme accretion, intrinsically weak/cool coronae, or heavy obscuration. SEAMBHs show Hα‑based Lbol underestimates SED‑based values, and SEAMBHs/LRDs/JWST-AGN share a high‑κbol,X regime indicating a relative X‑ray deficit. Caveat: many high‑z X‑ray points are upper limits and may miss heavy or Compton‑thick absorption, with sensitivity and steep spectra further suppressing detections.

Key figures to inspect

• L2–10 keV/LHα vs λEdd plane comparing SEAMBHs (baseline) with LRDs and JWST BL AGN—check how far high‑z sources sit below the SEAMBH locus and the strength/slope of the anti‑correlation for high‑λEdd objects.
• L2–10 keV vs LHα relation with censored points (upper limits) for high‑z sources—quantify the offset from standard local trends and how survival-analysis treatment changes the inference.
• κbol,X distributions (or κbol,X vs λEdd) across SEAMBHs, LRDs, and JWST BL AGN—verify the common high‑κbol,X regime that signals X‑ray deficit relative to bolometric output.
• SED‑based Lbol versus Hα‑based Lbol for SEAMBHs (with dust correction flagged)—measure the systematic underestimation when using Hα and its impact on placing high‑z analogs.
• Sample overview panel (SEAMBHs, NLS1s, BASS/SDSS type I, LRDs/JWST BL AGN)—inspect λEdd and redshift distributions to assess comparability and selection-driven biases.