Temperature evolution assuming ﹩\sigma _{xp}=\sigma _{0}( V/ V_{0}) ^{-4}﹩. The parameter ﹩\sigma _{0}﹩ is given by ﹩\sigma _{0}=10^{-25}m_{x}/ m_{p}\ \mathrm{cm}\,^{-2}﹩, and ﹩V_{0}=10^{3}\ \mathrm{km}\,\ \mathrm{s}\,^{-1}﹩. The solid, dotted, and dashed lines correspond to initial temperatures of 16, 8, and 3 keV, respectively. Thick and thin lines are for initial ﹩n_{p}﹩ of 0.015 and ﹩0.007\ \mathrm{cm}\,^{-3}﹩, respectively. For reference, the look‐back time to ﹩z=1﹩ is 8 Gyr.