The X-ray weakness of Little Red Dots and JWST-selected AGN: comparison with local AGN in different accretion regimes

TL;DR

This study compares high-redshift Little Red Dots and JWST-selected AGN with local AGN to understand their X-ray weakness, revealing links to accretion physics and observational challenges.

Contribution

It provides a comparative analysis of X-ray and optical properties of high-z and local highly accreting AGN, highlighting potential physical causes of X-ray weakness.

Findings

Some high-z sources resemble local super-Eddington accreting black holes.

Most high-z sources show suppressed X-ray emission, possibly due to extreme accretion or obscuration.

X-ray weakness correlates with high accretion rates and may be a common feature of highly accreting SMBHs.

Abstract

We investigate the origin of the observed X-ray weakness in high z LRDs and other JWST-selected broad line 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), NLS1s, and type I AGN from large surveys. We examine the relations between X-ray luminosity, broad H{\alpha} line luminosity, Eddington ratio, bolometric luminosity and X-ray-to-bolometric luminosity correction, and 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 SEAMBHs population in the $L_x/L_{H{\alpha}}$ versus $\lambda_{Edd}$ plane, most lie below it, suggesting either more extreme accretion conditions, suppressed coronal emission or heavy obscuration. We identify an anti-correlation between $L_x/L_{H\alpha}$ and $\lambda_{Edd}$ in the low z, high accreting subsample, consistent with theoretical expectations of slim-disc accretion. We further show that, for SEAMBHs, $H\alpha$-based bolometric luminosities underestimate SED-based values even after dust correction. We find that SEAMBHs, LRDs, and JWST-selected AGN occupy a similar high-$\kappa_{bol,x}$ regime, indicating that the relative deficit of X-ray emission compared to the bolometric output could potentially support the view that soft X-ray spectra arising from relatively cold coronae is a common feature of highly accreting systems across cosmic time. 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. 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.