We derive the nitrogen and oxygen abundances in the Narrow Line Regions (NLRs) of a sample of 38 local (z<0.4) Seyfert~2 nuclei. For that, we consider narrow optical emission line intensities and direct estimates of the electron temperatures (Te-method). We find nitrogen abundances in the range 7.6<12+log(N/H)<8.6 (mean value 8.06±0.22) or 0.4<(N/N⊙)<4.7, in the metallicity regime 8.3<12+log(O/H)<9.0. Our results indicate that the dispersion in N/H abundance for a fixed O/H value in AGNs is in agreement with that for disc \ion{H}{ii} regions with similar metallicity. We show that Seyfert~2 nuclei follow a similar (N/O)-(O/H) relation to the one followed by star-forming objects. Finally, we find that active galaxies called as 'nitrogen-loud' observed at very high redshift (z>5) show N/O values in consonance with those derived for local NLRs. This result indicates that the main star-formation event is completed in the early evolution stages of active galaxies.
@article{arxiv.2405.13906,
title = {Direct estimates of nitrogen abundance for Seyfert 2 nuclei},
author = {O. L. Dors and M. V. Cardaci and G. F. Hägele and M. Valerdi and G. S. Ilha and C. B. Oliveira and R. A. Riffel and S. R. Flury and K. Z. Arellano-Córdova and T. Storchi-Bergmann and R. Riffel and G. C. Almeida and I. N. Morais},
journal= {arXiv preprint arXiv:2405.13906},
year = {2024}
}