The X-ray weakness of little red dots and JWST-selected AGN: Comparison with local AGN in different accretion regimes

¹ INAF – Osservatorio astronomico di Roma, Via Frascati 33, I-00040 Monte Porzio Catone, Italy
² Department of Astronomy, University of Geneva, ch. d’Ecogia 16, 1290 Versoix, Switzerland
³ Instituto de Estudios Astrofìsicos, Facultad de Ingenierìa y Ciencias, Universidad Diego Portales, Av. Ejèrcito Libertador 441 Santiago, Chile
⁴ Key Laboratory for Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, 19B Yuquan Road, Beijing 100049, People’s Republic of China
⁵ Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy
⁶ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People’s Republic of China
⁷ Department of Astronomy, School of Physics, Peking University, Beijing 100871, People’s Republic of China
⁸ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
⁹ School of Astronomy and Space Sciences, University of Chinese Academy of Sciences, 19A Yuquan road, Beijing 100049, People’s Republic of China
¹⁰ National Astronomical Observatory of China, 20A Datun Road, Beijing 100020, People’s Republic of China
¹¹ European Southern Observatory (ESO), Alonso de Córdova 3107, Casilla 19 Santiago, Chile

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 26 September 2025
Accepted: 10 March 2026

Abstract

We investigate the origin of the observed X-ray weakness in high z little red dots (LRDs) and other JWST-selected broad line active galactic nuclei (AGN) by comparing their X-ray and optical properties with those of a diverse sample of low z AGN, including super-Eddington accreting massive black holes (SEAMBHs), narrow-line Seyfert 1 galaxies (NLS1s), and type I AGN from large surveys (e.g. BASS, SDSS). Using a heterogeneous set of AGN samples spanning a wide range of redshift and accretion rates, we examine the relations between X-ray luminosity (L_{2 − 10 keV}), broad Hα line luminosity (L_Hα), Eddington ratio (λ_Edd), bolometric luminosity (L_bol), and X-ray-to-bolometric luminosity correction (κ_bol, X), and we explore whether high z sources may represent analogues of local highly accreting systems. While a few LRDs and JWST-selected AGN are consistent with the SEAMBH population in the L_{2 − 10 keV}/L_Hα versus λ_Edd plane, most lie below it, suggesting either more extreme accretion conditions, suppressed coronal emission or heavy obscuration. We identify an anti-correlation between L_{2 − 10 keV}/L_Hα and λ_Edd in the low z, high-λ_Edd subsample of sources, consistent with theoretical expectations of slim-disc accretion. We further show that, for SEAMBHs, Hα-based bolometric luminosities underestimate spectral energy distribution-based values even after dust correction, reinforcing the need for SED-based estimates. We find that SEAMBHs, LRDs, and JWST-selected AGN occupy a similar high-κ_bol, X regime, indicating that the relative deficit of X-ray emission compared to the bolometric output could potentially support the view that suppression of the hot corona emission is a common feature of highly accreting systems across cosmic time. However, the X-ray measurements of high z sources are largely based on observed upper limits and generally do not account for heavy or Compton-thick obscuration, in which case the intrinsic L_{2 − 10 keV} could be substantially higher than observed. Our results are consistent with the idea that the observed X-ray weakness of LRDs and JWST-selected AGN may be linked to the physics of highly accreting SMBHs, but alternative explanations, including heavy obscuration, systematics in BH mass estimates, or a combination of intrinsic coronal suppression and absorption, remain viable. Moreover, observational limitations at high z, including instrumental sensitivity and the steep X-ray spectra expected for highly accreting systems, likely further suppress the detected X-ray signal. Disentangling the roles of accretion physics and obscuration will require deeper, higher-resolution X-ray observations with next-generation facilities, which will be crucial for establishing whether these sources represent genuine high z counterparts of local highly accreting AGN.