Two-dimensional histograms of the polarization fraction as a function of the circular variance for all the stacked maps at three wavelengths (from left to right λ = 0.8, 1.3 and 3.0 mm). Top row: results for the case where the alignment is computed according to the B-RAT theory along with the II and IDG mechanisms (B-RAT+II+IDG), as described in Sect. 2.4.3, while the bottom row shows the results for the case where dust grains are assumed to be perfectly aligned (PA) with the magnetic field.