The 157 μm cooling line intensity is calculated from Eq. (6) and is plotted as a function of the hydrogen number density and of the electron fraction (x = n_e / n_H). Note that the result should be scaled by the fraction of carbon in C⁺. The result should also be scaled by the carbon abundance with respect to the solar value and by the column density of hydrogen nuclei in units of 10²¹ cm^-2. For temperatures 50 K and 100 K, only the curve for x = 0 is shown.