Line ratio diagnostic diagrams involving Lyα, CIV, HeII, CIII], and CII] (adapted from De Breuck et al. 2000, their Fig. 13). The thick green cross shows the flux line ratios observed for Yggdrasil, while the circles show other HzRGs from the literature. Also shown are photo-ionisation and shock models to illustrate that the observed line ratios in Yggdrasil are dominated by photo-ionisation with a contribution of up to ~30% by shocks (see De Breuck et al. 2000, for more details).