Heating and cooling rate vs. redshift. Dashed lines show heating rate for halo of current mass 10¹⁰, 10¹¹, ﹩2\times 10^{12}﹩, ﹩10^{13}﹩, 10¹⁴, and 10¹⁵ M_⊙. Thick solid lines show the cooling rate at the virial radius assuming zero metallicity. Thin solid lines show the cooling rate at the virial radius assuming solar metallicity.