Top panel: absolute value of the cooling/heating function  | Γ − Λ |  for a hydrogen number density of n_H = 4.6 × 10^-3 cm^-3 corresponding to an overdensity of at z = 0.7 (solid line) and for a density of n_H = 9.2 × 10^-4 cm^-3 corresponding to an overdensity of (dashed line). The cooling function without heating is given in gray for comparison. Bottom panel: equilibrium temperature vs. density. In the range delimited by the two densities used in the top panel (emphasized by the the dashed lines) the relation can be approximated by a power law .