CH₃CHO/NH₂CHO column-density-ratio map along the L1157 southern outflow, assuming T_ex = 10 K across the entire outflow lobe. Regions where the emission is below 3σ are masked out (the corresponding 1σ RMS values are given in the caption of Fig. 1). The unitless colour scale is displayed at the top of the panel. Grey contours corresponding to the CS(2−1) velocity-integrated map are overlaid for reference, starting at 50σ and increasing in steps of 150σ. The black square at the top of the map marks the position of L1157-mm (Bachiller et al. 2001; Lefloch et al. 2017).