In situ mass fraction f_in, NSC versus galaxy mass for galaxies in Virgo and Fornax. The red line is the moving average (not considering the uncertainties in f_in, NSC) that crosses f_in, NSC = 50% for galaxy masses M_gal ∼ 1.5 × 10⁹ M_⊙. Bottom: mass-metallicity relation (MZR) of galaxies (Gallazzi et al. 2005; Kirby et al. 2013), with NSCs and host galaxy metallicities plotted in the coloured plus and star symbols from the measurements presented in Fahrion et al. (2021). Small grey plus symbols refer to other literature NSC metallicities as compiled in Neumayer et al. (2020).