Evolution of the halo half-mass radius R _h( t). The solid curves show the results of three subhalo-rich halos. The dashed curves show the results of three subhalo-poor halos. The left panel is for halos with 1.5 × 10 ¹²  M _☉ ⩽ M < 2.0 × 10 ¹²  M _☉. The right panel is for halos with 2.0 × 10 ¹²  M _☉ ⩽ M < 2.5 × 10 ¹²  M _☉.