Left panel: observed correlation between measures of CO(1-0) luminosity, L′_CO, and (8 − 1000 μm) IR luminosity, L_IR, for the samples of normal galaxies, SMGs, and QSOs at z > 1. For the three obscured QSOs described in this paper, we report the 3σ upper limits, as labelled. Open symbols refer to main sequence galaxies and SMG, filled symbols refer to QSOs. Where column density measurements are available, scaled star symbols indicate mild to high N_H values, as labelled in the right panel inset. Olive green symbols are the galaxies from Sargent et al. (2014); green symbols refer to SMGs from Bothwell et al. (2013), Coppin et al. (2008), and Silverman et al. (2015); red symbols refer to obscured targets. Optically bright QSOs are represented with blue dots. The solid curve represents the best-fit relation derived by (Sargent et al. 2014, 1σ scatter indicated with the grey area), for the MS galaxy sample they collected in the redshift range 0< z ≲ 3. Right panel: SFE vs. redshift for the same sample. In this panel, we labelled the names of the four sources from the literature associated with CT QSOs. The solid curve shows the 2-SFM predicted evolutionary trend of MS galaxies of M_star = 10¹¹ M_⊙ (shaded area: illustration of the scatter around the mean evolutionary trend for galaxies with SFR values 1σ above/below the MS). The long-dashed curve is located at 10-fold higher SFE than the mean MS evolutionary trend. Representative 1σ errors on individual data points are shown in the bottom left corner of the plots. For the two CT QSOs SW022513 and SW022550, Polletta et al. (2011) indicated a wide range for their IR luminosities (see Notes in Table C.2); these sources are therefore plotted in the left panel at the centroid of the IR range, while horizontal dotted lines show the IR luminosity interval. In the right panel we similarly reported the two sources at the centroid positions and indicated the SFE ranges with vertical dotted lines.