Age as a function of stellar mass. Navy points represent the members of the over-densities in CDFS, with circle shapes indicating galaxies with photometric redshifts and triangle-down shapes for those with spectroscopic redshifts Green points denote our identified passive galaxies. Light-red points correspond to passive galaxies from Merlin et al. (2019), at 3.01 < z < 3.9. Dark-red points represent passive galaxies from Straatman et al. (2014), at 3.46 < z < 4.05.