Distribution of IR-to-radio ratio (q_TIR) for SFGs in the Radio Sources Sample (upper row) and fractions of radio-excess AGNs (hosted by SFGs) in all the SFGs of the Radio Sources Sample (bottom row). Upper row: At each redshift bin (from left to right) the q_TIR distributions of the GOODS-N field and the COSMOS/UltraVISTA field are shown as the yellow histogram and the violet histogram, respectively. Each dotted curve represents each single-Gaussian model, while the solid curve represents the best-fit model to the entire q_TIR distribution. The vertical dashed line corresponds to the peak position of the highest Gaussian component. The vertical black dash-dotted line represents the threshold used in this work to separate SFGs and radio-excess AGNs (which corresponds to q_AGN in Fig. 3; see details in Section 4.1). Bottom row: At each redshift bin (from left to right) fractions of the radio-excess AGNs for the GOODS-N field and the COSMOS/UltraVISTA field are shown as the yellow dashed curve and the violet dotted curve, respectively. The parameter f_AGN is defined as 1 − N_SFG/N_TOT, where N_SFG represents the height of the highest Gaussian model (the highest dotted curve) at a certain q_TIR value, and N_TOT represents the height of the entire best-fit model (entire solid curve) at a certain q_TIR value. The vertical black dash-dotted line represents the threshold used in this work to separate SFGs and radio-excess AGNs (as in the upper panels).