Turnaround mass M_T(R) (in units of 10¹⁵h^-1M_⊙) versus radius of a sphere R in a spherical collapse model. The solid line corresponds to a flat model with Ω_m = 0.27 and grey dashed line to a model with Ω_m = 0.308. Filled circles show the total masses of galaxy groups in regions of different global density in the A2142 supercluster (Table 3). Stars denote estimated masses as explained in the text. The numbers show global density lower limits for each region.