Integrated intensity and PV diagrams of the blue (blue color bar) and red (red color bar) velocity components seen in N₂H⁺ (1–0), and of the H₂CO (2–1) emission (green color bar). Top left: spatial distribution of N₂H⁺ and H₂CO emission in G351.77. Markers and dashed gray lines are the same as in Fig. 11. The intersection of the dashed black lines represent the center of the rotating and infalling modeled sphere (see Appendix F). The ellipse in the bottom left represents the beam size of the N₂H⁺ data. Top right and bottom left: PV diagrams along the two perpendicular directions. The black contours represent the shapes shown by the rotating and infalling modeled sphere in the PV diagram.