Comparison of emission-line diagnostics for the two nuclei from SDSS data (left panels) and LBT long slits (right panels). Top panels: classical BPT diagnostic diagram with demarcation lines overplotted from Kewley et al. (2001; red line), Kauffmann et al. (2003a; blue line), and (Stasińska et al. 2008; green line), which define areas of star forming galaxies (SF), Seyfert galaxies, LINERs, and intermediate (inter) galaxies. Bottom panels: emission-line diagnostic diagram using the equivalent width of Hα replacing the [O III]/Hβ ratio following Cid Fernandes et al. (2010). The classification scheme for SF galaxies, strong AGN (sAGN), weak AGN (wAGN), and retired galaxies (RG) is adopted from Cid Fernandes et al. (2011). The nuclei with the brighter [O III] emission line are shown with filled symbols, while the corresponding fainter nuclei are denoted with open symbols.