Diagnostic diagrams for NGC 6762. From left to right: log ([Oiii]λ5007/Hβ) vs. log ([Nii]λ6584/Hα), log ([Oiii]λ5007/Hβ) vs. log ([Sii]λ6731,6717/Hα) and log ([Oiii]λ5007/Hβ) vs. log ([Oi]λ6300/Hα). The upper and bottom rows show the spaxels with F(Hα)/F(Hα)peak ≤ 0.20 and 0.20 ≲ F(Hα)/F(Hα)peak ≲ 1.00, respectively. The black solid curve (in all three panels) is the theoretical maximum starburst model from Kewley et al. (2001), devised to isolate objects whose emission line ratios can be accounted for by the photoionization by massive stars (below and to the left of the curve) from those where some other source of ionization is required. The black-dashed curves in the [Sii]λ6731,6717/Hα and [Oi]λ6300/Hα diagrams represent the Seyfert-LINER dividing line from Kewley et al. (2006) and transposed to the [Nii]λ6584/Hα by Schawinski et al. (2007). The predictions of different ionization models for ionizing the gas are overplotted in each diagram. The red lines represent the shock grids of Allen et al. (2008) with solar metallicity and preshock magnetic field B = 1.00 μG. For the grid of shock models, the solid lines show models with increasing shock velocity Vs = 100, 200, 300, 1000 km s-1, and dotted lines the grids with densities ne from 0.1 cm-3 to 100 cm-3. Grids of photoionization by an AGN (Groves et al. 2004) are indicated by green curves, with ne = 100 cm-3 and a power-law spectral index of − 1.4. The corresponding dashed-lines show models for Z = Z⊙ and Z = 2 Z⊙ (from left to right), and solid lines trace the ionization parameter log U, which increases with the [Oiii]λ5007/Hβ ratio from log U = −3.6, − 3.0, 0.0. We downloaded the shock and AGN grids from the web page http://www.strw.leidenuniv.nl/~brent/itera.html. The boxes show the predictions of photoionization models by pAGB stars for Z = Z⊙ and a burst age of 13 Gyr (Binette et al. 1994).
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