Left: (mid-IR based) AGN fraction α_AGN as a function of the ratio L_AGN/L_bol, with L_AGN = 3 × 10³L_[OIII] and L_bol = 1.15× L_IR. The nuclei of binary systems are connected with a vertical line; larger symbols refer to the sources with dominant AGN ionisation according to our BPT diagnostics. Right: [O III] and Na ID non-parametric velocity w80 as a function of the AGN fraction α_AGN, defined on the basis of mid-IR diagnostics (Sect. 1). Each nucleus is identified with a distinct colour, as in Fig. 6.