The radio properties of the JWST-discovered AGN

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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 3 σ upper limit at rest frame 5 GHz of L 5GHz = 2 × 10 39 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.

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