Polar map of the velocity residuals. Same as Fig. 4, but now overlaid with filamentary structures found by FilFinder. The overplotted red and blue lines are the medial axes of the filamentary structures found by the algorithm. To trace the apparent spiral in the residuals, we restricted the algorithm to search for filaments in the radial locations r = [0.3, 1.25]″. For the filamentary detection, we assumed a smoothing size of one synthesized beam size and a minimum size of 500 pixels for a filament to be considered.