Radial profiles of azimuthally averaged column density for the three groups of coalescing filaments identified in Fig. A.2. We note that these are profiles obtained on the filament-component map masked by detected skeletons. These groups encompass a larger number of filaments at larger distances while narrowing down on individual filaments closer to the centre. Readers should notice that the slopes of the radial profiles changes once at ~0.8 pc and again at ~0.2 pc. At larger distances from the centre, it is not possible to discern noticeable effects. The vertical lines at 3 pc, 1.3 pc, and 0.85 pc correspond to the two outermost red circles (nodes), the red circle just above the black cone, and the outer boundary of the black cone in Fig. 2a, respectively. They demarcate the two steps of coalescence suggested in Sec. 4.1