Polarization data at 1.3 mm wavelength for IRDC18310-4. The left panel shows the Stokes I emission (4σ contours of 0.6 mJy beam⁻¹), and the middle panel presents the linearly polarized emission (4σ contours of 24 μJy beam⁻¹). The line segments show the corresponding polarization angles (the magnetic field should be rotated by 90 °). The right panel shows for comparison the polarization fraction in color with the same contours of linearly polarized emission as in the middle panel. The polarization fraction should be considered as an upper limit because Stokes I may be more strongly affected by interferometric spatial filtering than the weaker polarized emission.