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arXiv · 2405.13906

Direct estimates of nitrogen abundance for Seyfert 2 nuclei

O. L. Dors·M. V. Cardaci·G. F. Hägele·M. Valerdi·G. S. Ilha·C. B. Oliveira·R. A. Riffel·S. R. Flury·K. Z. Arellano-Córdova·T. Storchi-Bergmann·R. Riffel·G. C. Almeida·I. N. Morais
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Abstract

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 ($T_{\rm e}$-method). We find nitrogen abundances in the range $7.6 \: < \: \rm 12+log(N/H) \: < \: 8.6$ (mean value $8.06\pm0.22$) or $\rm 0.4 \: < \: (N/N_{\odot}) \: < 4.7$, in the metallicity regime $8.3 \: < \: \rm 12+log(O/H) \: < \: 9.0$. 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.

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O. L. Dors, M. V. Cardaci, G. F. Hägele, M. Valerdi, G. S. Ilha, C. B. Oliveira, R. A. Riffel, S. R. Flury, K. Z. Arellano-Córdova, T. Storchi-Bergmann, R. Riffel, G. C. Almeida, I. N. Morais. 2024-05-22. Direct estimates of nitrogen abundance for Seyfert 2 nuclei. https://arxiv.org/abs/2405.13906

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