Star formation histories. Stacked mass-weighted age distributions of the stellar populations for BL and BD galaxies, subdivided by stellar mass and by whether the galaxy experienced a major merger (top panel). Stacked mass-weighted age distributions relative to the time of the major merger for galaxies that have suffered just a major merger since z = 2 (bottom panel). Shaded regions denote the 20^th − 80^th percentile range, while vertical solid lines indicate the median star age at which 50% of the z = 0 stellar mass was assembled. BL galaxies generally host younger stellar populations compared to BD galaxies, regardless of merger history.