Chemical abundances of Seyfert 2 AGNs – II. N2 metallicity calibration based on SDSS

• Published in: Monthly notices of the Royal Astronomical Society Vol. 492; no. 4; pp. 5675 - 5683
• Main Authors: Carvalho, S P, Dors, O L, Cardaci, M V, Hägele, G F, Krabbe, A C, Pérez-Montero, E, Monteiro, A F, Armah, M, Freitas-Lemes, P
• Format: Journal Article
• Language: English
• Published: Oxford University Press 11.03.2020
• Subjects: galaxies: formation; galaxies: Seyfert; galaxies: active; galaxies: evolution; galaxies: ISM; galaxies: abundances; galaxies: nuclei
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/staa193

ABSTRACT We present a semi-empirical calibration between the metallicity (Z) of Seyfert 2 active galactic nuclei and the N2 = log([N ii]λ6584/H α) emission-line intensity ratio. This calibration was derived through the [O iii]λ5007/[O ii]λ3727 versus N2 diagram containing observational data and photoionization model results obtained with the cloudy code. The observational sample consists of 463 confirmed Seyfert 2 nuclei (redshift $z \: \lesssim 0.4$) taken from the Sloan Digital Sky Survey DR7 data set. The obtained Z–N2 relation is valid for the range $0.3 \: \lesssim \: (Z/{\rm Z}_{\odot }) \: \lesssim \: 2.0$ that corresponds to $-0.7 \: \lesssim \: ({\rm N}2) \: \lesssim \: 0.6$. The effects of varying the ionization parameter (U), electron density and the slope of the spectral energy distribution on the Z estimations are of the order of the uncertainty produced by the error measurements of N2. This result indicates the large reliability of our Z –N2 calibration. A relation between U and the [O iii]/[O ii] line ratio, almost independent of other nebular parameter, was obtained.