Σ_SFR against stellar mass density for M 51 (physical scale of 153.4 pc). The blue density distribution represents the pixels that belong to M 51a, the green distribution corresponds to the pixels of the tidal bridge, and the red distribution denotes the pixels of M 51b within a 2 kpc radius. The black line is the relation presented in Enia et al. (2020), the purple line is the best-fitting relation from MaNGA (Cano-Díaz et al. 2019), and the pink line is for galaxies in the CALIFA survey (Cano-Díaz et al. 2016). The remaining coloured lines are a fit through the distribution of the same colour.