BPT spatially resolved diagrams for the regions of NGC 5077 where ionised gas (Hβ, [O III], Hα, [N II], and [S II]) is significantly detected. Left panel: colour-coded regions to facilitate the identification of spatial trends. Panels b and c: each show a different line ratio diagnostic, and panel d shows the Hα equivalent width as a function of [N II]/Hα (‘WHAN’) diagram. The labels and the solid or dashed lines indicate the plausible excitation mechanisms in each region of the diagram (see the text for a description). The coloured symbols match the line ratios measured for the corresponding colour-coded regions of the left panel. The diagrams show that there is a dominant contribution of AGN excitation in most of the regions (green circles and light blue crosses). The dark blue crosses show regions where post-AGB stars make an equal or larger contribution than the AGN to the ionising field.