Channel maps of the ¹²CO J = 2 → 1 line from the PdBI mosaic. The contours are 1 to 9 by 1  ×  0.1 Jy per 056  ×  042 beam (4.5σ, 9.91 K). The V_LSR is marked in each panel in km s^-1. The red cross marks the stellar location. Cyan arcs mark the CO spirals identified in Sect. 3.3.1. The S4 arm is a dotted arc, because it does not have as broad a linewidth as S1, S2, and S3.