The C II cooling function vs. n _H of the ISM gas within 0.1 kpc (left panel), 0.2 kpc (middle panel), and 0.3 kpc (right panel) around Cluster-3. The dotted–dashed line is the ﹩\propto {n}_{{\rm{H}}}^{2}﹩ relation and the dashed line is the ∝ n _H relation to guide the eye. As can be seen, the majority of the ISM close to Cluster-3 is thermalized and thus collisionally de-excited. This causes the gas to be [C II] deficit in the vicinity of Cluster-3.