Scatter plot displaying the relationship between metallicity, [Fe/H], and stellar ages, t_★, using UNIDAM estimates for the entire sample. Data points are categorised by HC groups. On top, 1D-Gaussian kernel densities show age distribution; on the right, a similar view presents [Fe/H] distribution for each HC group. The window width for the kernel density estimation is computed using Scott’s method, with a default bandwidth adjustment of 1, which is the standard configuration of the SEABORN package in PYTHON (Waskom 2021); this configuration is consistently applied to all figures with Gaussian kernel densities throughout this paper. The data points and densities are colour-coded and stratified according to the different HC groups, similarly to Fig. 1.