The observed dust polarisation and the inferred orientation of the plane-on-the-sky magnetic fields in SPT0346–52. (a–c) are the maps of Stokes parameters I, Q, and U. The ellipse with diagonal hatching in a) shows the size of the final clean beam (0.38″ × 0.3″). The light blue vectors (without direction) show the orientation of the magnetic fields, with their length proportional to the polarised fraction. A legend of a 2% polarisation fraction is shown in the bottom right corner of panel a). In all the maps, the white contours show the signals at a certain significance level relative to the RMS of the noise. The dashed contour indicates the negative value, while solid contours show the positive levels. In Stokes I, the white contours start at 5σ level of the RMS and increase with a step of 20σ (σ=12 µJy beam⁻¹). The contours of Stokes Q and U start at 3σ and increase with a step of 2σ. (d) shows the linear polarised intensity. The contours start at 3σ and increase with a step of 2σ (σ=8.5 µJy beairr⁻¹). The detection of polarised dust emission indicates that SPT0346–52 has already developed kiloparsec-scale ordered magnetic fields at ɀ=5.6.