Feature space projected on the third and fourth principal components (PC₃ on the x- and PC₄ on the y-axis). As in Fig. 4, each symbol represents a mock observation, obtained from a snapshot. Different simulation runs are harder to distinguish in this projection, so the labels used in Fig. 4 have been dropped. Empty red symbols correspond to merger simulations, filled black symbols to monolithic simulations. Mergers and monolithic observations appear systematically different in PC₄.