Spatial distribution of galaxies at z = 3 around the most massive cluster in TNG300 (Group 0, see Table 1, same as Figure 1). Orange stars show the cluster member (CM) galaxies that underwent a recent major merger – defined as a mass ratio of 1:n (n≤4) – in the last 200 Myr while blue circles indicate those that did not (C-Gal). The dark matter distribution at the thickness of 60 cMpc is shown in the background. The black circles are the same shown in Figure 1, indicating the farthest galaxy position, R₂₀₀ at z = 3, and R₂₀₀ at z = 0.