Rotation measure of the filaments. Left: high spatial resolution (7.4″ × 7.3″) RM map. The local Galactic Faraday rotation has been subtracted (ϕ = 39.5 rad m⁻²). Black contours are the same as in Fig. 8 but at levels (20, 50, 100, 200)×σ. Right: more detailed look at the Faraday depth structure within the box of the left panel, using three planes from the deconvolved Faraday depth cube. After subtracting a Galactic contribution of 39.5 rad m⁻², the respective Faraday depths were red = 8.5, green = 20.5, and blue = 32.5 rad m⁻². There is sometimes emission at more than one Faraday depth at the same location, producing other colours, but they do not correspond to a single Faraday depth (or RM).