Diagnostic plots for GMM clustering model selection. According to our validation metrics, the best candidate number of clusters are N = 4, N = 6 for NG73 and N = 3, N = 5 for NG76 (compare Fig. 1). Panels a–d: show the clustering results of these choices. The models in a) (N = 4) and d) (N = 5) trace the over- and underdensities in the domain best and we consider them our nominal models.