[C II] luminosity L_[C II] as a function of H₂ mass M_H2 (dark pink), H I mass M_HI (orange), and H II mass M_HII (green) at z = 10 (top) and 6 (bottom). The dashed lines show the median value for CDM HR, and the darker (lighter) shaded regions represent the 1σ (2σ) standard deviation. The solid dark pink line represents the fit to the CDM HR results for M_H2, the solid orange line shows the fit for M_HI, and the green line shows M_HII (see the text). The solid red and black lines show the linear fit to post-processed SIMBA simulations for M_H2 and M_HI in their validity range (see Vizgan et al. 2022a,b), and the extrapolations of the fit to lower masses is highlighted with dotted lines. We highlight the redshift evolution of the linear relation between log₁₀(L_[C II]) and log₁₀(M_H2), log₁₀(M_HI), and log₁₀(M_HII). Moreover, we find that H I is always the dominant phase for COLDSIM galaxies.