Classic FP of PLCK-G287 with points colored as a function of the stellar mass (left panel) and residuals of the classic FP as a function of M^⋆ (right panel). Gray points are the ETGs used to fit the FP. A linear fit (solid black line) shows a clear relation between M^⋆ and the residuals. As a reference, we also show the average residuals (blue points) computed in five bins of equal width of the stellar mass, which are indicated by the vertical dashed gray lines. The value of $\overline{R^2}=0.96$ and the Spearman’s rank correlation coefficient ρ = 1 with a p-value of 0.001, computed using these binned residuals, confirm the linear relation with the stellar mass.