Velocity-coded ¹³CO map. The color image shows the velocity distribution of the emission peak of ¹³CO. The black long arrow indicates the axis of the position–velocity map in Figure 8. The black dot on the axis indicates the position of the ionizing star. An azimuthally averaged (around the ionizing star within the sector region) position–velocity map is given in Figure 9. The positions of four filamentary structures are shown with white lines.