C II cooling function vs. number density for the ISM gas within 1 kpc from Cluster-3 for the t = 170 Myr snapshot (see Figure 1). The top left panel shows all contributing ISM gas. The dotted–dashed line shows the ﹩\propto {n}_{{\rm{H}}}^{2}﹩ relation, while the dashed line shows the ∝ n _H relation to guide the eye. The rest of the panels show how each different ISM component (as defined in Section 4) contributes to the total Λ_CII. In general, collisional de-excitation does not play an important role in the overall Λ_CII function. The color-coding represents the distribution of SPH mass within the studied region.