Age-metallicity distributions for the M 54 star cluster. Top left: the ground truth number density from individual measurements of resolved stars in M 54, from Alfaro-Cuello et al. (2019). Top right: a MAP revovery using PPXF full spectrum fitting of an integrated-light M 54 spectrum, from B20. Bottom row: results of ULoG on M 54 data using low-regularisation. Both panels show the same MAP estimate of the recovered posterior probability density. The coloured circles show the location of significant blobs with 95%-credibility, with colours as in Fig. 3. The left shows results using SVD-MCMC, the right shows Full MCMC. In both cases, ULoG identifies 3 distinct blobs with 95%-credibility.