Stellar population properties and SFH of UDG1. Top panel: MUSE 1 R_e stacked spectrum (solid black line) for UDG1. The main absorption features are marked in purple. The solid red line represents the best fit obtained with ppxf. The green points denote the residuals between the observed spectrum and its best-fit template spectrum. The grey areas indicate the masked regions excluded from the fit. Bottom left panel: Age-metallicity distribution of the MC iterations of UDG1. Bottom right panel: Cumulative mass fraction, based on the MC iterations. t₅₀ marks the time at which 50% of the galaxy mass was formed.