BPT diagnostic diagram showing the emission-line ratios log([N II]/Hα) versus log([O III]/Hβ) for the SDSS-selected sample. The demarcation curves from Kauffmann et al. (2003), Kewley et al. (2001), and Cid Fernandes et al. (2010) are shown to separate star-forming, composite, LERG, and HERG regimes. Sources located below the dash–dotted orange line are classified as LERGs (green triangles), while those above are classified as HERGs (black pentagons).