Line-of-sight hydrogen column density vs. galaxy separation. The blue circles, green triangles, orange diamonds, red stars, and purple triangles denote the AGNs in stage A, B (early mergers), C, D (late mergers), and N (nonmergers) U/LIRGs, respectively. Single nuclei in merging (stage D) and nonmerging (stage N) sources are plotted on the left and right sides, respectively. The black dotted and dashed lines denote ﹩{N}_{{\rm{H}}}^{\mathrm{LoS}}={10}^{22}﹩ and 10²⁴ cm⁻², respectively. The unobscured AGNs (NGC 7469 and NGC 7679) are assigned upper limits of ﹩{N}_{{\rm{H}}}^{\mathrm{LoS}}﹩ = 10²⁰ cm⁻².