Unveil the nature of JWST-AGN and Little Red Dots with SKAO continuum surveys

Giovanni Mazzolari, Dharam V. Lal, Isabella Prandoni, Roberto Gilli, Roberto Maiolino, Hannah Übler, Ivan Delvecchio, Marcella Brusa, Marco Mignoli

First listed 2026-07-01 | Last updated 2026-06-29

Abstract

The advent of JWST has revealed a large population of AGN at $z>4$, which are $\sim1$ dex more abundant than previously expected, including also the enigmatic population of Little Red Dots (LRDs). Remarkably, the vast majority of JWST-discovered AGN and LRDs are not detected in X-rays, and most of them also show faint rest-frame UV continua and faint high-ionization emission lines, as well as unusually faint emission in the Mid and Far infrared. Recent studies investigating their radio properties have reported no significant detections, even in deep stacking analyses, reaching sensitivities of 0.5-0.1 $μ$Jy at $z\sim 5-6$, corresponding to $L_{R}\lesssim 10^{39}\rm \ erg\ s^{-1}$. While these non-detections may be consistent with a standard radio-quiet nature, some results suggest that the radio emission might instead be significantly suppressed by other physical phenomena. Three main scenarios have been proposed in the literature to explain the physical properties of these objects across the electromagnetic spectrum: Compton-thick absorption by a broad-line region with high covering-factor, intrinsically weak emission driven by high accretion rates, or the presence of a cocoon of dense ionized gas that produces strong scattering effects. The unprecedented sensitivity of SKAO will enable the detection of the radio emission of these AGN in all three cases. Because each scenario is expected to produce distinct radio signatures, future SKAO continuum surveys will be able to distinguish between them, uncovering the physical processes responsible for their peculiar properties. Observations spanning a wide range of integration times (1-1000 hours) and frequencies with SKA-Mid and SKA-Low (0.2-11 GHz) will allow us to characterize these objects from the local Universe to high redshift, investigate possible radio variability, and test alternative scenarios to black hole accretion.

Short digest

This paper lays out how SKAO continuum surveys can break the current degeneracy in the nature of JWST-selected z>4 AGN and Little Red Dots, a population now inferred to be about 1 dex more abundant than pre-JWST expectations but still largely invisible in X-rays and radio stacks. Using the existing picture of faint rest-UV continua, weak high-ionization lines, and radio non-detections down to roughly 0.5-0.1 μJy at z∼5-6, the authors frame three main explanations: Compton-thick high-covering-factor BLR obscuration, intrinsically weak emission from very high accretion rates, or strong scattering inside a dense ionized cocoon. Their main result is that SKA-Low and SKA-Mid observations across 0.2-11 GHz and 1-1000 hour integrations should detect these sources in all three scenarios while separating them through their different radio SED shapes, depths, and possible variability. That makes the radio a decisive route to testing whether LRDs are genuinely AGN-powered, heavily buried, intrinsically X-ray weak, or governed by dense circumnuclear gas that suppresses their emission across other bands.

Key figures to inspect

• Figure 1. Use this as the observational-motivation figure. It compiles the failed radio stacking attempts for photometrically selected LRDs and spectroscopically confirmed Type I JWST AGN, making the present upper-limit landscape immediately clear and showing why a step change in sensitivity is needed.
• Figure 2. This is the key diagnostic figure of the paper. It compares the predicted radio SEDs for the three physical scenarios against SKAO detection limits across multiple bands and integration times, while also showing the host-galaxy star-formation contribution, so it directly encodes how SKAO can discriminate between obscuration, intrinsically weak accretion-powered emission, and electron-scattering suppression.
• Figure 3. Include this as the concrete falsifiability figure. By plotting expected 1.4 GHz luminosities for GOODS-N JWST Type I AGN under the assumption that the full H emission is due to star formation, then comparing them with current VLA and future SKAO Band-2 limits, it shows how SKAO can test non-AGN interpretations for the bulk of the sample.