Intrinsic column density (derived assuming Γ = 1.8) as a function of Log(λ_Edd). QSOs from the HC-WISSH sample with available M_BH are plotted. WISSH BAL objects are contoured with a turquoise line. X-ray-weak QSOs (Δ(α_OX) <  − 0.2) are surrounded with a green circle. Blue and red QSOs are shown in the corresponding colour. Stars correspond to sources for which intrinsic absorption is significantly detected (see Sections 3.1.1 and 3.1.2). QSOs from Ricci et al. (2017) are shown as grey crosses. Black solid and dashed lines are Ishibashi et al. (2018) and Fabian et al. (2008) relations, derived from a maximal- and no-photon trapping model, respectively. The black horizontal dotted line indicates N_H = 10²² cm⁻².