Portion of combined 1D NIR spectrum around Hβ and [O III] emission lines. Top panel: contribution from the off-trace spatially extended emission, which is apparent in both [O III] lines. Bottom panel: spectrum collapsed over its full spatial extent at wavelengths 1.790 <  λ(μm) < 1.825 and the optimal extraction elsewhere, for presentation purposes. The green line shows our estimate of featureless continuum emission. Individual Gaussians constrained during the fit are shown in different colours, with the total fitted profile shown in red.