The radio properties of the JWST-discovered AGN

¹ Dipartimento di Fisica e Astronomia, Universitá di Bologna Via Gobetti 93/2 I-40129 Bologna, Italy
² INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna Via Gobetti 93/3 I-40129 Bologna, Italy
³ Kavli Institute for Cosmology, University of Cambridge Madingley Road Cambridge CB3 0HA, UK
⁴ Cavendish Laboratory, University of Cambridge 19 JJ Thomson Avenue Cambridge CB3 0HE, UK
⁵ Department of Physics and Astronomy, University College London Gower Street London WC1E 6BT, UK
⁶ INAF – Istituto di Radioastronomia Via Gobetti 101 I-40129 Bologna, Italy
⁷ The William H. Miller III Department of Physics & Astronomy, Johns Hopkins University Baltimore MD, USA
⁸ Space Telescope Science Institute for the European Space Agency (ESA), ESA Office 3700 San Martin Drive Baltimore MD, USA
⁹ National Radio Astronomy Observatory, 520 Edgemont Road Charlottesville VA 22903 USA
¹⁰ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónomia de México, Antigua Carretera a Pátzcuaro # 8701 Ex-Hda. San José de la Huerta Morelia Michoacán C.P 58089, Mexico
¹¹ Max Planck Institut für Astronomie Königstuhl 17 D-69117 Heidelberg, Germany
¹² National Radio Astronomy Observatory Observatory, 1011 Lopezville Rd., P.O. Box O Socorro, NM 87801, USA
¹³ Dipartimento di Fisica e Astronomia, Universitá di Firenze via G. Sansone 1 50019 Sesto Fiorentino Firenze, Italy
¹⁴ INAF – Osservatorio Astrofisico di Arcetri Largo Enrico Fermi 5 I-50125 Firenze, Italy
¹⁵ Dipartimento di Matematica e Fisica, Univeristá di Roma 3, Via della Vasca Navale 84 00146 Roma RM, Italy
¹⁶ Institute of Astronomy, University of Cambridge Madingley Road CB3 0HA, UK
¹⁷ Max-Planck-Institut für extraterrestrische Physik (MPE) Gießenbachstraße 1 85748 Garching, Germany
¹⁸ Jodrell Bank Centre for Astrophysics, School of Physics & Astronomy, The University of Manchester, Alan Turing Building Oxford Road Manchester M13 9PL, UK

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Received: 5 December 2024
Accepted: 1 August 2025

Abstract

The James Webb Space Telescope (JWST) has discovered a large population of active galactic nuclei (AGN) in the early Universe. A large fraction of these AGN revealed a significant lack of X-ray emission; the observed X-ray luminosity upper limits were 2–3 dex lower than expected. We explored the radio emission of these AGN, focusing on the JWST-selected broad-line AGN (BLAGN, or type 1) in the GOODS-N field, one of the fields with the best combination of deep radio observations and statistics of JWST-selected, spectroscopically confirmed BLAGN. We used deep radio data at different frequencies (144 MHz, 1.5 GHz, 3 GHz, 5.5 GHz, 10 GHz), and we find that none of the 37 sources investigated is detected at any of these frequencies. Similarly, the radio stacking analysis does not reveal any detection down to an rms of ∼0.15 μJy beam⁻¹, corresponding to a 3σ upper limit at rest frame 5 GHz of L_5GHz = 2 × 10³⁹ erg s⁻¹ at the mean redshift of the sample z ∼ 5.1. We compared this and the upper limits of the individual sources with expected radio luminosities estimated assuming different AGN scaling relations to check whether they are consistent with the standard BLAGN spectral energy distribution. For most of the sources the radio luminosity upper limits are still compatible with expectations for radio-quiet (RQ) AGN; nevertheless, the more stringent stacking upper limits and the fact that no detection is found might suggest that JWST-selected BLAGN are weaker than standard AGN, even at radio frequencies. The probability of having none of the BLAGN detected in none of the investigated radio images is expected to be on average very low (P < 10⁻⁴). We discuss some scenarios that could explain the possible radio weakness, such as free-free absorption from a dense medium or the lack of either a magnetic field or a corona, possibly as a consequence of super-Eddington accretion. These scenarios would also explain the observed X-ray weakness. We also conclude that ∼1 dex more sensitive radio observations are needed to better constrain the level of radio emission (or lack thereof) for the bulk of these sources. The Square Kilometer Array Observatory (SKAO) will likely play a crucial role in assessing the properties of this AGN population.