Same as Fig. 2, but for the ¹³CO emission, and the high-velocity range for the ¹³CO emission is V_LSR = 1.9–3.8 and 10.3–12.8 km s^-1. Black and green dots delineate the ridges of the contour lines, showing the arc structures. The ridges of the contour lines were measured from the peak positions of the intensity profiles along the transverse directions of the arc structures. Green dots with labels A–H mark the positions of the extracted spectra show in Fig. 4. Gray scales in panels c and d present the moment 0 map of the CO (1–0) emission observed with ALMA, and the map is obtained from the data released by ALMA Partnership et al. (2015). Contour levels are 5σ, 15σ, and 30σ in the high-velocity blueshifted map, are 5σ, 15σ, 35σ, and 55σ in the high-velocity redshifted map, are 5σ, 15σ, 25σ, 45σ, and 75σ in the medium-high-velocity maps, are 5σ, 10σ, 15σ, 25σ, 35σ, 45σ, and 75σ in the medium-low-velocity maps, and are 5σ, 10σ, 15σ, 20σ, and 60σ in the low-velocity maps. The noise level in the high-velocity blue- and redshifted map is 5.8 and 7.1 mJy Beam^-1 km s^-1, respectively, and the levels in the other maps are all 4.1 mJy Beam^-1 km s^-1. Significant flux is missing in the velocity ranges of panels c and d, as shown in Figs. B.1 and B.2. The negative contours are not plotted in panels c and d for clarity.