Sketch showing how the CO ν = 1–0 band emission is produced in the outflow region of NGC 3256 S. The ~4.7 μm photons from the dust around the AGN (brown lines) illuminate the molecular clouds (blue ellipse). These photons are absorbed by CO molecules, which are excited to the ν = 1 levels and decay through the P- and R-branches (orange lines). The CO ν = 1-0 absorption is only observed in lines of sight that intersect both the ~4.7 μm continuum source and the molecular clouds.