Abstract We derive the helium and oxygen abundances in the Narrow Line Regions (NLRs) of 84 Active Galactic Nuclei (AGNs) spanning two redshift ranges: 65 objects at z 0. 2 and 19 objects at 2. 8 ≲ z ≲ 6. 8. Spectroscopic data in the optical rest-frame range 3000 λ (Å) 7000 from the JADES survey and from the literature were used to estimate He/H and O/H via the Te-method (7 objects) and strong-emission line calibrations (19 objects). Our results indicate that the ionization degree in AGNs increases toward higher redshifts, exhibiting a trend similar to that observed in star-forming galaxies. We find that the majority of our sample of AGNs at z 2. 8 show oversolar helium abundances and subsolar oxygen abundances. We identified, via the Te-method, an object (goods-s-mediumhst-58850; z = 6. 2615) with the highest helium abundance estimated to date, i. e. 12 + log (He/H) = 11. 64, corresponding to (He/He) 4. 4. This result remains robust even when we adopt larger electron densities (varying Ne from 500 to 10 000 cm^-3) in abundance estimates using the Te-method and empirical strong-line methods. We found marginal evidence for a decline in the He/H abundance (~0. 04 dex per redshift unit) toward lower redshifts. In contrast, we found evidence for an increase in O/H toward the local universe at a rate of approximately 0. 06 dex per redshift unit.
Dors et al. (Fri,) studied this question.