Comparison of IRAS16399−0937 regions with galaxies exhibiting starburst activity or AGN in mid-IR diagnostic diagrams. Top panel: 6.2 μm/7.7 μm vs. 11.3 μm/7.7 μm PAH flux ratios. The dashed lines represent theoretical loci for neutral and ionized PAHs (Draine & Li 2001). The dot-dash line shows the locus of molecules formed by 240 carbon atoms. Points representing the integrated spectrum of the IRAS16399−0937 system, the IRAS16399N and IRAS16399S nuclei and the ISM sub-regions are plotted using the symbols shown in the key. Bottom panel: 7.7 μm/11.3 μm PAH flux ratio plotted vs. [Ne III] 15.5/[Ne II] 12.8 μm. This diagram is used as an indicator of the hardness of the radiation field (e.g., Smith et al. 2007; Sales et al. 2010; Baum et al. 2010). As the [Ne III] 15.5 μm line falls in the IRS LL spectrum, which does not resolve the two nuclei, or the ISM sub-regions, only the point representing the integrated spectrum of IRAS16399−0937 is plotted in this diagram. In both panels, the galaxy data are taken from the sample compiled by (Sales et al. 2010; see also Smith et al. 2007; Brandl et al. 2006; Gallimore et al. 2010): empty triangles represent H II galaxies and LINERs; filled triangles are starburst galaxies; filled and empty circles are Seyfert 1 and 2 galaxies, respectively.