Maps of the emission line ratios commonly used in the classical diagnostic diagrams. First row: [N II]λ6583/Hα (left), [S II]λ6717,6731/Hα (middle), and [S II]λ6717/[N II]λ6583 (right), which is commonly analyzed in studies of the DIG. Second row: [O I]λ6300/Hα (left) and [O III]λ5007/Hβ (middle), as well as the η′ parameter (right) as described in Sect. 3.2 and defined in Appendix B, which quantifies the distance to the Kewley et al. (2001) starburst limit in the [O III]/Hβ vs. [S II]/Hα diagnostic diagram. The black demarcation lines in the η′ map separate bins below the starburst limit (η′≤0.5) from bins above that limit (η′> 0.5). The gray and white contours are at the same equidistant arbitrary levels from the synthetic V-band image as in Fig. 3.