BPT diagrams used to classify narrow emission-line galaxies. GALEX Lyα emitters are represented with black circles with corresponding error bars, together with an IUE sample of local starburst galaxies in blue squares. The left panel shows [Oiii] λ5007/Hβ versus [Nii] λ6584/Hα ratios. The dashed and solid curves are theoretical boundaries separating starbursts and AGN objects assuming an instantaneous burst (Dopita et al. 2000) and an extended star formation episode (Kewley et al. 2001), respectively. The dotted curve is the “Kauffmann line” (Kauffmann et al. 2003). The right panel represents the [Oiii] λ5007/Hβ versus [Sii] (λ6717 + 6732)/Hα diagnostic with the same theoretical models as in the right panel. The red dot-dashed line shows typical model uncertainties of ± 0.1 dex. The diagram includes all the 11 IUE local galaxies, among which is an object previously classified as an AGN (red square) that we decided to show as an example.