1. Empirical calibration for helium abundance determinations in Active Galactic Nuclei
- Author
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Dors, O. L., Almeida, G. C., Oliveira, C. B., Flury, S. R., Riffel, R., Riffel, R. A., Cardaci, M. V., Hägele, G. F., Ilha, G. S., Krabbe, A. C., Arellano-Córdova, K. Z., Santos, P. C., and Morais, I. N.
- Subjects
Astrophysics - Astrophysics of Galaxies - Abstract
For the first time, a calibration between the HeI $\lambda5876$/H$\beta$ emission line ratio and the helium abundance $y$=12+log(He/H) for Narrow line regions (NLRs) of Seyfert~2 Active Galactic Nuclei (AGN) is proposed. In this context, observational data (taken from the SDSS-DR15 and from the literature) and direct abundance estimates (via the $T_{\rm e}$-method) for a sample of 65 local ($z \: < \: 0.2$) Seyfert~2 nuclei are considered. The resulting calibration estimates the $y$ abundance with an average uncertainty of 0.02 dex. Applying our calibration to spectroscopic data containing only strong emission lines, it yields a helium abundance distribution similar to that obtained via the $T_{\rm e}$-method. Some cautions must be considered to apply our calibration for Seyfert~2 nuclei with high values of electron temperature ($\gtrsim\: 20\,000$ K) or ionization parameter ($\log U > -2.0$)., Comment: Accepted for publication as Letter in MNRAS
- Published
- 2024