See text for a general description of the figure. NGC 4374: in the HST/STIS spectrum, [S II] lines are severely blended, and only the [O I]λ6300 Å line is visible (with low S/N). This complicated the modeling for the other lines, so the fit was performed considering the narrow peaks of [N II]−Hα blend (see Sect. 3), which results in high residuals under the [S II] lines. A broad component is needed in this decomposition. For the Palomar spectrum, all the emission lines are well-modeled with two Gaussian components.