Theoretical predictions of the β‐﹩r_{c}﹩ relation in the case of (a) ﹩\Omega _{0}=1.0﹩, ﹩\gamma =1﹩ and (b) ﹩\Omega _{0}=0.2﹩, ﹩\gamma =1﹩, for ﹩T_{1}=0.5﹩ (dashed line), 1 (solid line), and 2 keV (dotted line). The arcs AD and BC correspond to ﹩M_{\mathrm{vir}\,,0}=5\times 10^{15}\,M_{\odot }﹩ and ﹩5\times 10^{14}\,M_{\odot }﹩, respectively. The segment AB corresponds to ﹩z_{\mathrm{coll}\,}=0﹩, and the segment CD corresponds to ﹩z_{\mathrm{coll}\,}=0.5﹩ in (a) and ﹩z_{\mathrm{coll}\,}=4﹩ in (b). The observational data obtained by Mohr et al. (1999; filled circles) and Peres et al. (1998; open squares) are overlaid.