N2 index vs. EW_Hα. Blue points show all the Hα candidates. Black and golden circles represent sources with an [N II] line flux above and below OTELO flux limit, respectively (see Sect. 3.2 and Bongiovanni et al. 2020). Red circles show AGN candidates selected using the Stasińska et al. (2006) empirical limit of N2 = −0.4. Vertical green and blue dashed lines show the Yin et al. (2007) and Pettini & Pagel (2004) limits of their calibration using the N2 index, respectively. The red line shows the AGN selection limit from Stasińska et al. (2006). The error bars in each object correspond to the 25% and 68% confidence interval around the most probable value.