Polarization fraction p as a function of the normalized Stokes I, that is I/I_max, where I_max is the maximum value of the intensity at each wavelength. The dots show the values obtained with a sampling of 0″.15 that fulfill the following requirements: I > 0.2 mJy beam⁻¹ and > 0.8 mJy beam⁻¹ at 3.1mm and 1.3mm, respectively, and polarized intensity higher than 0.03 mJy beam⁻¹ and 0.06 mJy beam⁻¹, respectively. The red line is only for illustration and indicates p =(Stokes I/I_max)⁻¹.