Left: blown-up image of the 850 µm Stokes I emission towards the hub of W3 Main (in units of Jy/beam), overlaid by normalized POS B-field lines. Grey contours display VLA 6 cm emission at 0.1″ resolution; the symbols A, B, C, and D mark the known compact HII regions. The youngest most luminous source IRS 5 is also indicated. The white arcs aid visualization of the organized B-field pattern. The white star and arrow indicate the centre of a CO outflow and its direction, respectively (see text for details). Right: W3 foreground mini-HFS, also referred to as W3 Main SE, indicated with the square on the left panel. The Spitzer three colour image is overplotted with Stokes I contours and normalized POS B-field line.