Articulo
Chemical abundances of Seyfert 2 AGNs – III. Reducing the oxygen abundance discrepancy
Registro en:
issn:0035-8711
issn:1365-2966
Autor
Dors, Oli L.
Maiolino, Roberto
Cardaci, Mónica Viviana
Hägele, Guillermo Federico
Krabbe, Angela
Pérez-Montero, Enrique
Armah, M.
Institución
Resumen
We investigate the discrepancy between oxygen abundance estimations for narrow-line regions of active galactic nuclei (AGNs) type Seyfert 2 derived using direct estimations of the electron temperature (Te-method) and those derived using photoionization models. In view of this, observational emission-line ratios in the optical range (3000<;λ(A˚)<7000) of Seyfert 2 nuclei compiled from the literature were reproduced by detailed photoionization models built with the CLOUDY code. We find that the derived discrepancies are mainly due to the inappropriate use of the relations between temperatures of the low (t₂) and high (t₃) ionization gas zones derived for H II regions in AGN chemical abundance studies. Using a photoionization model grid, we derived a new expression for t₂ as a function of t₃ valid for Seyfert 2 nuclei. The use of this new expression in the AGN estimation of the O/H abundances based on Te-method produces O/H abundances slightly lower (about 0.2 dex) than those derived from detailed photoionization models. We also find that the new formalism for the Te-method reduces by about 0.4 dex the O/H discrepancies between the abundances obtained from strong emission-line calibrations and those derived from direct estimations. Instituto de Astrofísica de La Plata
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