VMC galaxy overdensity map of the N-E region of the PClJ1001 + 0220 proto-cluster (see details in Sect. 3.2). The VUDS spectral members of the system are indicated with white diamond symbols, while the location of our merging system and a possibly associated additional member observed with DEIMOS are indicated with a cyan star and a blue square, respectively. Overplotted on the map are overdensity isopleths at significance levels of [4, 6, 8, 10, 11.5, 13]σ, where σ is calculated as the RMS fluctuation of the overdensity field over the entire map (see Cucciati et al. 2018; Hung et al. 2020). The map shows that the merging system studied in this work is clearly located close to an overdensity peak of the proto-cluster. The black solid bar shows a reference length of 500 kpc.