Simulated projected maps of gas surface density, centered on the infalling group B (black diamond marking its center), at z = 0.25 (left) and z = 0.07 (right). The gas surface density map encloses a comoving volume of (4 cMpc/h)³. In both panels, we mark the circles corresponding to three times the GC1 cluster virial radius and R₂₀₀ of the group at z = 0.25 (solid) and of the GC1 cluster at z = 0.07 (dot-dashed; when group B is a substructure of GC1).