Age dependence of the M_MUSE/L_3.6 μm ratio (in M_⊙/L_⊙) for the galaxies in our sample, where L_3.6 μm corresponds to the luminosity of a pixel in the original IRAC 3.6 μm image (not the ICA version from S⁴G). Each line represents a galaxy, coloured by its total stellar mass. The figure shows a positive trend, with pixels hosting older stellar populations having larger M/L ratios. The horizontal lines mark different values adopted in the literature (dot-dashed line M/L = 0.41, Schombert et al. 2019; dotted line, M/L = 0.53, Eskew et al. 2012; dashed line M/L = 0.6, Meidt et al. 2014).