Left: N_H column density map derived from the C¹⁸O (J = 1−0) integrated intensity (multi-Gaussian model). The orientation of the magnetic field, derived from Planck polarimetric data, is shown by the black segments. The spacing of the segments corresponds to the 5′ beam of Planck. Middle: map of the ratio of the C¹⁸O-traced N_H to the dust-traced N_H above 3 magnitudes of A_V in Orion B. Superimposed are contours of the C¹⁸O (J = 1−0) integrated intensity at 0.75, 2.5 and 7.5 K km s⁻¹. Right: effective dust temperature map computed by Lombardi et al. (2014). The black segments again show the orientation of the magnetic field.