Corner plot of uncertainties of age, [M/H] and [Mg/Fe] for a spatial bin with S/N ∼ 40. The plotted 1σ-uncertainty distributions result from fitting with pPXF 10 000 Monte Carlo perturbations of the observed spectrum, with 2 different multiplicative polynomials and 3 different regularization parameters. These uncertainties were calculated as the difference between the (weighted-average) individual values of age, [M/H] or [Mg/Fe] and the median value of all the 60 000 fits.