Intrinsic X-ray luminosity versus obscuring column density for DRC-2 (red symbol) compared with several sub-populations of AGN. Only objects detected in the X-rays are included. Hot dust-obscured galaxies (Hot DOGs; purple symbols) are collected from Stern et al. (2014), Assef et al. (2016), Ricci et al. (2017), Vito et al. (2018), and Zappacosta et al. (2018). Red Type 1 QSOs (or Extremely Red QSOs, ERQs, green symbols) are from Urrutia et al. (2005), Banerji et al. (2014), Mountrichas et al. (2017), Goulding et al. (2018), and Lansbury et al. (2020). Type 1 QSOs (blue symbols) are collected from Just et al. (2007, arbitrarily placed at log N_H = 21.5) and Martocchia et al. (2017). Dust obscured galaxies (DOGs) and SMGs (black symbols) are collected from Wang et al. (2013), Corral et al. (2016), and Zou et al. (2020). Grey symbols represent X-ray selected AGN population in the Chandra deep field-south (Li et al. 2019), with typical error bars showed in the lower right corner of the figure. Leftward pointing arrows represent upper limits on the column density.