Another view into JWST-discovered X-ray weak AGNs via radiative dusty feedback

W. Ishibashi, A. C. Fabian, R. Maiolino, Y. Gursahani, C. S. Reynolds

First listed 2025-09-05 | Last updated 2025-09-05

Abstract

JWST has revealed a previously unknown population of low-luminosity active galactic nuclei (AGN) in the early Universe. These JWST-AGN at high redshifts are characterised by a set of peculiar properties, including unusually weak X-ray emission. Here we investigate the apparent lack of X-ray emission in the framework of the ``AGN radiative dusty feedback'' scenario based on the effective Eddington limit for dust. We analyse how the boundary in the $N_\mathrm{H} - λ$ plane, defined by the column density versus the Eddington ratio, is modified as a function of the dusty gas parameters (metallicity, dust grain size and composition). Low metallicity gas with little dust content tends to survive against radiation pressure, and likely accumulates in the nuclear region. We suggest that such dust-poor gas can provide long-lived absorption and may lead to heavy X-ray obscuration, as observed in early JWST-AGN. The blowout vs. stalling condition of the obscuring clouds indicates that higher metallicities are required to eject heavier column densities, while large columns of gas can stall in low metallicity environments. Therefore the metallicity may play a key role in the AGN radiative dusty feedback scenario. We discuss how other peculiar properties of JWST-AGN -- such as Balmer absorption features and weak radio emission -- may be naturally interpreted within the same physical framework.

Short digest

The authors revisit the X-ray weakness of JWST-selected AGN by mapping dusty gas dynamics onto the N_H–λ plane using the effective Eddington limit for dust. Varying metallicity, grain size, and composition shifts the critical boundary: low-Z, dust-poor gas resists radiation pressure, enabling long-lived nuclear absorption and heavy X-ray obscuration consistent with early JWST-AGN and LRDs. The blowout vs. stalling analysis shows that higher metallicity is needed to expel larger columns, whereas substantial columns stall at low Z, making metallicity a key regulator of obscuration. The framework also naturally links Balmer absorption features and weak radio emission to the same radiative dusty feedback physics.

Key figures to inspect

• Fig. 1: N_H–λ boundary vs metallicity—inspect how decreasing Z shifts the curve right, shrinking the forbidden (blowout) region and enlarging the long-lived obscuration zone.
• Panels varying dust grain size/composition—compare graphite vs silicate and MRN cutoffs to see how UV/IR opacities move the IR- and UV-limited segments of the boundary, and where the single-scattering regime causes overlap at intermediate N_H.
• Blowout versus stalling map—read off the Z required to eject given N_H; note the region where N_H ≳ 10^23–10^24 cm^-2 stalls at low Z but is expelled at higher Z.
• Application plot placing JWST-AGN/LRDs in the N_H–λ plane—locate typical λ and inferred/required N_H against the long-lived obscuration region to gauge consistency with X-ray non-detections and stacking limits.