Chemical abundances of Seyfert 2 AGNs – IV. Composite models calculated by photoionization + shocks

  • O L Dors
    Universidade do Vale do Paraíba, Av. Shishima Hifumi, 2911, Cep 12244-000 São José dos Campos, SP, Brazil
  • M Contini
    School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
  • R A Riffel
    Universidade Federal de Santa Maria, Av. Roraima 1000, Cep 97105-900 Santa Maria, Brazil
  • E Pérez-Montero
    Instituto de Astrofísica de Andalucía, Camino Bajo de Huétor s/n, Aptdo. 3004, E-18080 Granada, Spain
  • A C Krabbe
    Universidade do Vale do Paraíba, Av. Shishima Hifumi, 2911, Cep 12244-000 São José dos Campos, SP, Brazil
  • M V Cardaci
    Instituto de Astrofísica de La Plata (CONICET-UNLP), La Plata, Avenida Centenario (Paseo del Bosque) S/N, B1900FWA, Argentina
  • G F Hägele
    Instituto de Astrofísica de La Plata (CONICET-UNLP), La Plata, Avenida Centenario (Paseo del Bosque) S/N, B1900FWA, Argentina

抄録

<jats:title>ABSTRACT</jats:title> <jats:p>We build detailed composite models of photoionization and shock ionization based on the suma code to reproduce emission lines emitted from the Narrow Line Regions (NLR) of Seyfert 2 nuclei. The aim of this work is to investigate diagram active galactic nucleus (AGN) positions according to shock parameters, shock effects on the gas temperature and ionization structures and derive a semi-empirical abundance calibration based on emission-line ratios little sensitive to the shock presence. The models were used to reproduce optical (3000 &lt; λ(Å) &lt; 7000) emission line intensities of 244 local ($z \: \lesssim \: 0.4$) Seyfert 2s, whose observational data were selected from Sloan Digital Sky Survey DR7. Our models suggest that shocks in Seyfert 2 nuclei have velocities in the range of 50–300 $\rm km \: s^{-1}$ and imply a narrower metallicity range ($0.6 \: \lesssim \: (Z/Z_{\odot }) \: \lesssim \: 1.6$) than those derived using pure photoionization models. Our results indicate that shock velocity in AGNs cannot be estimated using standard optical line ratio diagrams, based on integrated spectra. Our models predict a different temperature structure and $\rm O^{+}$/O and $\rm O^{2+}$/O fractional abundances throughout the NLR clouds than those derived from pure photoionization models, mainly in shock-dominated objects. This suggests that, in order to minimize the shock effects, the combination of emission-lines emitted by ions with similar intermediate ionization potential could be good metallicity indicators. Finally, we derive two calibrations between the N/O abundance ratio and the N2O2 = log([N ii]λ6584/[O ii]λ3727) and N2 = log([N ii]λ6584/H α) indexes which agree with that derived from pure photoionization models.</jats:p>

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