Galactic N_H versus the observed N_H for our high-z sample, estimated from the XMM2ATHENA 4XMM catalogs of X-ray spectral properties. The red, dashed line shows the one-to-one relation. Grey, solid circles are sources with an observed N_H consistent with the galactic N_H. The black, open circles show sources with N_H robustly above the Galactic value (the lower limit of the 90% confidence interval is higher than the Galactic N_H). The blue circles mark the optically selected QSO identified by Yang & Shen (2023) also included in our sample. The plot only includes sources where our estimated 90% confidence interval for the observed log N_H is narrower than 3 dex (501 out of 801 sources).