Intrinsic X-ray luminosity in the 2−10 keV band versus hydrogen column density. Small circles show the full sample from Pouliasis et al. (2024), shaded by the probability of being CTK. Large circles mark our selection of CTK candidates, as described in Sect. 2.1, colour-coded according to their parent X-ray survey: CDF (yellow), CCLS (red), XXL-N (blue). For clarity, error bars (indicating 90% credible intervals) are shown only for the CTK candidates.