We show the evolution of the mass-weighted distribution of the Mach number ﹩{ \mathcal M }﹩ of the detected shocks within a 1 h ⁻¹ cMpc sphere around the galaxy halo. The colors represent the redshift, as indicated in the labels. The transition from the accretion-shock-dominated regime at high redshift to the internal-shock-dominated regime at low redshift can be clearly seen.