Emission-line diagnostic diagrams: [O III]λ5007/H_β versus three different line ratios (BPT; Baldwin et al. 1981; Kewley et al. 2001, 2006; Kauffmann et al. 2003) and W_Hα versus [N II]λ6584/H_α (WHAN; Cid Fernandes et al. 2011). The lines demarcate boundaries between sources classified as star-forming (SF) galaxies, AGNs, low-ionization nuclear emission-line regions (LINERs), “Composite” sources, weak AGNs (wAGN), strong AGNs (sAGN), retired galaxies (RG) and passive galaxies. Classifications based on SDSS observations are indicated by blue squares, while red circles indicate the classifications based on Palomar and Keck observations. Numbers refer to source identifications in Table 1.