BPT types of the fibre spectra in NGC 3521. Panela: BPT diagram for the individual fibres in NGC 3521. The blue symbols denote the fibres with H II-region-like spectra, the red symbols mark the fibres with intermediate BPT-type spectra, and the black symbols are the fibres with AGN-like spectra. The solid and short-dashed curves mark the demarcation lines between AGNs and H II regions defined by Kauffmann et al. (2003) and Kewley et al. (2001), respectively. The long-dashed line is the dividing line between Seyfert galaxies and LINERs defined by Cid Fernandes et al. (2010). Panelb: Distribution of the fibres with different BPT-type spectra across the image of NGC 3521. The BPT types of spectra are colour-coded as in panel (a). The circle shows the kinematic centre of the galaxy, the line indicates the position of the major kinematic axis of the galaxy, and the ellipse corresponds to the optical radius of the galaxy.