Effect of the CMB on the Gao–Solomon relation at z = 3 for a range of kinetic temperatures with ﹩{\bar{n}}_{{{\rm{H}}}_{2}}=1\times {10}^{4}﹩ cm⁻³ (left) and ﹩{\bar{n}}_{{{\rm{H}}}_{2}}=1\times {10}^{5}﹩ cm⁻³ (right), calculated using RADEX. Data from Gao et al. (2007) and references therein: Beelen et al. (2006), Carilli et al. (2005), Solomon & Vanden Bout (2005), Wagg et al. (2005), Egami et al. (2000), Riechers et al. (2006), Isaak et al. (2004), and Greve et al. (2006).