JWST-discovered AGN: Evidence of heavy obscuration in the type 2 sample from the first stacked X-ray detection

¹ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna (OAS) Via Gobetti 93/3 I-40129 Bologna, Italy
² Dipartimento di Fisica e Astronomia (DIFA), Università di Bologna Via Gobetti 93/2 I-40129 Bologna, Italy
³ Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics Clemson SC 29634, USA
⁴ Kavli Institute for Cosmology, University of Cambridge Madingley Road Cambridge CB3 OHA, UK
⁵ Cavendish Laboratory – Astrophysics Group, University of Cambridge 19 JJ Thomson Avenue Cambridge CB3 OHE, UK
⁶ Department of Physics and Astronomy, University College London Gower Street London WC1E 6BT, UK
⁷ Max-Planck-Institut für extraterrestrische Physik (MPE) Gießenbachstraße 1 85748 Garching, Germany
⁸ Dipartimento di Fisica e Astronomia, Università di Firenze Via G. Sansone 1 I-50019 Sesto Fiorentino Firenze, Italy
⁹ INAF – Osservatorio Astrofisico di Arcetri Largo Enrico Fermi 5 I-50125 Firenze, Italy

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Received: 28 August 2025
Accepted: 21 December 2025

Abstract

One of the most puzzling properties of the high-redshift active galactic nucleus (AGN) population recently discovered by JWST, including both broad-line and narrow-line sources, is their X-ray weakness. With very few exceptions, and regardless of the optical classification, they are undetected at the limits of the deepest Chandra fields, even when stacking signals from tens of sources in standard observed-frame energy intervals (soft, hard, and full bands). It has been proposed that their elusive nature in the X-ray band is due to heavy absorption by dust-free gas or an intrinsic weakness, possibly due to high super-Eddington accretion. For this work we performed X-ray stacking in three customized rest-frame energy ranges (1–4, 4–7.25, and 10–30 keV) of a sample of 50 type 1 and 38 type 2 AGN identified by James Webb Space Telescope (JWST) in the Chandra Deep Field South (CDFS) and Chandra Deep Field North (CDFN) fields. For the type 2 subsample, we achieve a total exposure of about 210 Ms, and report a significant detection (∼3σ) in the hardest band (10–30 keV rest frame), along with relatively tight upper limits in the rest-frame softer energy bands. The most straightforward interpretation is in terms of heavy obscuration due to gas column densities well within the Compton-thick regime (> 2 × 10²⁴ cm⁻²) with a large covering factor, approaching 4π. The same procedure applied to the type 1 subsample returns no evidence of a significant signal in about 140 Ms stacked data in any of the adopted bands. The bolometric correction k_bol to the absorption corrected 2–10 keV X-ray luminosity of type 2 AGN is consistent with the average value obtained for X-ray selected type 2 objects in the literature. The lower limit on k_bol for the type 1 sample is significantly higher and inconsistent with that of type 2 objects. Absorption in the Compton-thick regime or extreme X-ray weakness, would bring the current lower limits closer to the observed values for type 1 X-ray selected AGN. A brief comparison with the current observations and the implications for the evolution of AGN are discussed.