Chemical abundances of Seyfert 2 AGNs I. Comparing oxygen abundances from distinct methods using SDSS

• Main Authors: Dors, O. L, Freitas-Lemes, P, Amores, E. B, Perez-Montero, E, Cardaci, M. V, Hagele, G. F, Armah, M, Krabbe, A. C, Faundez-Abans, M
• Format: Journal Article
• Language: English
• Published: 09-12-2019
• Subjects: Physics - Astrophysics of Galaxies
• DOI: 10.48550/arxiv.1912.04236

We compare the oxygen abundance (O/H) of the Narrow Line Regions (NLRs) of
Seyfert 2 AGNs obtained through strong-line methods and from direct
measurements of the electron temperature (Te-method). The aim of this study is
to explore the effects of the use of distinct methods on the range of
metallicity and on the mass-metallicity relation of AGNs at low redshifts (z <
0.4). We used the Sloan Digital Sky Survey (SDSS) and NASA/IPAC Extragalactic
Database (NED) to selected optical (3000 < A < 7000) emission line intensities
of 463 confirmed Seyfert 2 AGNs. The oxygen abundance of the NLRs were
estimated using the theoretical Storchi-Bergmann et al. calibrations, the
semi-empirical N2O2 calibration, the bayesian Hii-Chi-mistry code and the
Te-method. We found that the oxygen abundance estimations via the strong-line
methods differ from each other up to ~0.8 dex, with the largest discrepancies
in the low metallicity regime (12 + log(O/H) . 8.5). We confirmed that the
Te-method underestimates the oxygen abundance in NLRs, producing unreal
subsolar values. We did not find any correlation between the stellar mass of
the host galaxies and the metallicity of their AGNs. This result is independent
of the method used to estimate Z.