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
astro-ph.GA, astro-ph.CO
Submitted: 2026-06-29
Comments: Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366). Report-no:AASKAII/Mazzolari01
License: http://creativecommons.org/licenses/by-nc-sa/4.0/
The gist: The advent of JWST has revealed a large population of AGN at z>4, which are about1 dex more abundant than previously expected, including also the enigmatic population of Little Red Dots (LRDs).
Terminology
Abstract
The advent of JWST has revealed a large population of AGN at z>4, which are about1 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 mu Jy at z about 5-6, corresponding to L R 10 39 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.
Sources
- How similar are narrow-line Seyfert 1 galaxies and high-z type 1 AGN?
- Impact of Resonance, Raman, and Thomson Scattering on Hydrogen Line Formation in Little Red Dots
- [Ne v] emission from a faint epoch of reionization-era galaxy: evidence for a narrow-line intermediate mass black hole
- Uncertainties in high-$z$ galaxy properties inferred from SED fitting using JWST NIRCam photometry
- Overmassive black holes and little red dots naturally form in simulations
- Little Red Dots host Black Hole Stars: A unified family of gas-reddened AGN revealed by JWST/NIRSpec spectroscopy
- Active galactic nuclei-heated dust revealed in "little red dots"
- BlackTHUNDER strikes twice: rest-frame Balmer-line absorption and high Eddington accretion rate in a Little Red Dot at $z=7.04$
- Irony at z=6.68: a bright AGN with forbidden Fe emission and multi-component Balmer absorption
- A high black hole to host mass ratio in a lensed AGN in the early Universe
- A JWST/NIRSpec First Census of Broad-Line AGNs at z=4-7: Detection of 10 Faint AGNs with M_BH~10^6-10^8 M_sun and Their Host Galaxy Properties
- Extremely Dense Gas around Little Red Dots and High-redshift Active Galactic Nuclei: A Non-stellar Origin of the Balmer Break and Absorption Features
- The $M_{\rm BH}-M_{*}$ Relationship at $3<z<7$: Big Black Holes in Little Red Dots
- JADES -- The Rosetta Stone of JWST-discovered AGN: deciphering the intriguing nature of early AGN
- A dormant, overmassive black hole in the early Universe
- JADES: comprehensive census of broad-line AGN from Reionization to Cosmic Noon revealed by JWST
- The Rise of Faint, Red AGN at $z>4$: A Sample of Little Red Dots in the JWST Extragalactic Legacy Fields
- Challenging the AGN scenario for JWST/NIRSpec LRD and non-LRD broad H$\alpha$ emitters in light of non-detection of NIRCam photometric variability and X-ray
- A candidate supermassive black hole in a gravitationally-lensed galaxy at $z\approx10$
- The case for super-Eddington accretion in JWST broad-line AGN during the first billion years
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