Cumulative hydrogen column density in the direction of Suzaku src B (left) and XMMU J170147.3−421407 (right). The shaded gray region indicates the total level of systematic uncertainties, due the assumption of an average conversion factor X_CO = 1.5 × 10²⁰ cm⁻² (K km s⁻¹)⁻¹ (Strong et al. 2004), which impacts the H₂ measurement up to 30%, and an optically thin medium which can lead to underestimations of the HI content up to factor of 2 (Lau et al. 2018). The red band indicates the modeled column density required by the X-ray observations, with statistical errors only (see Table 1).