Correlations of σ_z with stellar age at fixed metallicity (left), and stellar metallicity at fixed age (right) for, from top to bottom, the three galaxies studied in this work, and the field S0 NGC 3115 (Poci et al. 2019). The curves are coloured by their age/metallicity bin corresponding to those of Figs. 10–12. The Spearman rank coefficient r and the associated p-value, computed for all curves collectively in a given panel, are inset. The shaded regions correspond to the variations derived from 100 Monte Carlo fits to the stellar population maps. The stellar AVR at fixed metallicity exhibits lower significance than the [Z/H] − σ_z at fixed age.