The giant H ii complex LHA 120-N 51 in the light of [S ii] (red), Hα (green), and [O iii] (blue), all data from MCELS (see Sect. 2.3). The red box delineates the area shown in Fig. 2. Noticeable substructures are : DEM L205 (A), the SNR candidate analysed in this paper; N51A (B) and N51C (C, also named DEM L201), two H ii regions also seen in the radio and the IR; the SB N51D, or DEM L192, in (D).