X-ray derived column densities (x-axis) vs. ISM column densities obtained with a uniform spherical model (y-axis). The values related to the SMG CO-SLED, the QSO CO-SLED, and the continuum emission method are indicated by the red circles, blue circles, and green diamonds, respectively. We also report on the y-axis (black open squares) the column densities derived from the SED fitting by Circosta et al. (2019). The source IDs are reported in orange. The black dashed line represents the N_HX = N_HISM curve. The error bars correspond to the 1σ significance level, while the upper limits are given at the 3σ level. For clarity the horizontal error bars of the X-ray derived column densities are reported only on the black open squares.