Search for a second parameter in the TFR. The plot shows the Spearman rank correlation coefficients for the correlations between ΔM, the residual between the actual absolute magnitude and the magnitude expected from the TFR, and eight different galaxy properties, as a function of the broadband. Extensive galaxy properties are shown in blue hues, intensive properties in red hues. The grey band corresponds to |r_s|< 0.4, usually considered as the region of negligible to weak correlations.