Beyond the BPT diagnostic diagrams

Two-dimensional strong-line BPT diagnostic diagrams have been very useful at differentiating objects dominated by different ionization mechanisms. However, there are much more we can learn about different classes of objects by using multi-dimensional diagnostics, using weak lines, and using spatial and kinematic information. I will present our recent results on the studies of ionization mechanisms of two classes of objects: Seyferts and LINER-like (aka LIER) objects. For Seyferts, I will present a method for breaking the line ratio degeneracy between metallicity variation in Seyferts and star formation contamination. For LINER-like objects, I will present temperature and abundance measurements for the warm ionized gas in quiescent galaxies, which provide additional clues on the puzzle of their ionization mechanisms.