BPT spectral diagnostic diagram for 727 host galaxies with narrow emission-lines. Star forming (SF) and composite galaxies are displayed with green triangles and orange circles, respectively. The blue asterisks and red squares respectively are Seyferts and LINERs. The red solid line shows the theoretical demarcation line separating AGN from SF galaxies proposed by Kewley et al. (2001, K01), while the green dashed line is the empirical line proposed by Kauffmann et al. (2003, K03). The magenta dotted line is the Seyfert-LINER demarcation line proposed by Cid Fernandes et al. (2010, C10). The underlying density distribution of the SDSS emission-line galaxies is shown in grayscale. The grayscale bar in the right represents the number of galaxies in each density bin.