Emission-line ratio diagnostic diagram for recombination lines of Brγ at 2.166 μm and He I lines at 2.058 and 2.120 μm. The region occupied by the black points corresponds to the values expected from the shock models of Sutherland & Dopita (2017). The filled stars are IRAS 15103−5754 (blue), IRAS 15445−5449 (green), and IRAS 18443−0231 (red). The sizes of the symbols are larger than their errors. The arrows indicate upper limits for the flux of the He I 2.120 μm emission line (see Fig. 1 and Table B.1).