Left panel: overlay of the R′ band (0.626 μm) Q_φ reflected light (which is not scaled by r²) and 880 μm map from ALMA Cycle 0 observations (contour lines every 10...90% peak of the 880 μm continuum emission) of J1604. Right panel: radial profile of the polarised surface brightness (arbitrary units), and the comparison with the size of the mm-cavity observed with ALMA at 880 μm (Zhang et al. 2014). The cavity radius inferred from CO J = 3−2 emission is also displayed. The error bars correspond to the standard deviation at each position from calculating the mean value at each radius from the centre of the image.