Temperature evolution with different metallicities Z and cooling options by metals. The meaning of the lines is as follows: high Z and no cooling by metals (solid line), low Z and no cooling by metals (dotted line), high Z and cooling by metals included (dashed line), low Z, and cooling by metals included (dashed-dotted). The dashed-dotted and dotted lines overlap. Top panel: the H₂ cooling is enabled. Bottom panel: the H₂ cooling is switched off. The cooling by Cen (1992) is switched off in both panels.