Emission lines diagnostic diagrams. The curves show the separation between star-forming galaxies and AGN at redshift z = 0 (grey) and z = 2.3 (black) from Kewley et al. (2013a). In the cases where one line is not detected (S/N < 3), the line ratio is shown with an arrow indicating a 5σ upper (or lower) limit. In the cases where both the Hα and [N II] lines are not detected, the [N II]/Hα line ratio is unconstrained (see box on the right). Upper panel: the line ratios are measured from the total emission line profile. Lower panel: the line ratios are calculated using the fluxes of only the narrow Gaussian component. For the three targets for which the emission lines were fitted with only one Gaussian component (marked with black crosses), the line ratios are the same as in the upper panel.