Distribution of IR-radio-ratio (q_TIR) in SFGs (left column) and QGs (right column) at different redshift bins. The q_TIR distributions were obtained by merging the Radio Sources Sample from the GOODS-N and COSMOS/UltraVISTA fields. Each yellow dotted curve represents a single-Gaussian model, while the black solid curve represents the best-fit model to the entire q_TIR distribution. The vertical black dashed line (corresponding to the ${\overline{q}}_{\mathrm{TIR}}$ value in the figure) represents the peak position of the highest Gaussian component. The vertical red dash-dotted line (corresponding to the q_AGN value in the figure) represents the cross point between the highest Gaussian component and the second-highest Gaussian component, which is used as the threshold to separate SFGs and radio-excess AGNs in this work. For QGs at 2.0 < z ≤ 4.0, it is difficult to find a best-fit model due to the low source number, so here the threshold at 0.1 < z ≤ 0.5 was used, which does not have a significant effect on the results.