Table 1.
Main assumptions behind the calibrators drawn from the literature.
| Authors | Nitrogen secondary-origin | Ionizing continuum | Gas density & gas pressure | Solar abundance |
|---|---|---|---|---|
| SB98 | logN/O = 0.96 × (12 + logO/H) – 9.26 (Storchi-Bergmann et al. 1994) | “Table AGN” in CLOUDY, using a typical observed AGN continuum (a combination of power laws; see Mathews et al. 1987). | nH = 300 cm−3 | 12+log (O/H)⊙ = 8.9 (Aller 1987) (Grevesse et al. 1984) |
| C20 | logN/O = 1.29 × (12 + logO/H) – 11.84 (Dors et al. 2017) | slope ≤ −1.4 between 2 keV and 2500 Å | Ne = 100,500,3000 cm−3 | 12+log(O/H)⊙ = 8.69 (Asplund et al. 2009) |
| T18 | logN/O = −1.73 × (log O/H + 2.19) (Nicholls et al. 2017) | NLR ionizing spectrum with the energy of the peak of the accretion disk emission −2.0 ≤ logEpeak ≤ −1.25, photon index of the inverse Compton scattered power-law tail, Γ = 2, and the proportion of the total flux that goes into the non-thermal tail, pNT = 0.15 (Thomas et al. 2016) | log(P/k)=5 | 12+log(O/H)⊙ = 8.76 (Nicholls et al. 2017) |
| This work | log (N/H) = −4.57 + log (Z/Z⊙) for log (Z/Z⊙) ≤−0.63; log (N/H) = −3.94 + 2 ⋅ log (Z/Z⊙) otherwise (Dopita et al. 2000) | power law continuum from TABLE POWER LAW command in CLOUDY with slope α = −2 at hν≥ 3676 Ryd | nH = 100 cm−3 | 12+log(O/H)⊙ = 8.69 (Asplund et al. 2009) |
Notes. Summary of the main assumptions to derive the calibrators and models retrieved from the literature, used to make a comparison with Eq. (3) describing the AGN calibrator presented in this work. Columns are: (i) relation for the nitrogen secondary origin (+ reference paper); (ii) ionization continuum to model the emission from the AGN’s accretion disk; (iii) gas density and/or gas pressure; and (iv) reference value assumed for the solar abundance.
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