N_H histogram with a bin width of 0.5 dex. Top panel: A red histogram represents eFEDS-DOGs. Second panel: A blue histogram represents eFEDS-undetected PL DOGs, indicating lower limits on log(N_H/cm⁻²). Note that only this panel uses a different binning scheme: 22.0–23.0, 23.00–23.25, and 23.25–23.50. Third panel: Lime, green and purple histograms represent Lanzuisi et al. (2009), Corral et al. (2016) and Riguccini et al. (2019), respectively. Fourth panel: Magenta, cyan, and pink histograms represent Toba et al. (2020), Zou et al. (2020), and Kayal & Singh (2024), respectively. Bottom panel: black, gray, and brown histograms represent Assef et al. (2016), Ricci et al. (2017a), and Zappacosta et al. (2018), respectively.