Column densities of dark matter, stars, and gas (from top to bottom) in a cutout from the IllustrisTNG100 simulation containing the infalling group of galaxies at t = 4 Gyr (z = 1.6). The images are centered on galaxy ID96543, the galaxy ID96527 is visible to the left of it, and ID96526 is beneath it. The BCG of the forming cluster, into which the group is infalling, is visible in the upper left part of each panel.