Left: velocity-integrated ¹²CO J = 2−1 line emission in color scale (blue scale for the 68–80.3 km s^-1 spectral range and orange for the 80.3–94 km s^-1 interval) superimposed on the optical image obtained with the Hubble Space Telescope (Hubble Legacy Archive 2013). More details can be found in Sect. 3 and Fig. 1. Right: brightness ¹²CO J = 3−2 emission at the central velocity (LSR velocity 80.4 km s^-1, after integrating in 0.4 km s^-1) in contours overlaid on the optical image in color scale. Contours are plotted at 4 ×σ, and from 10 ×σ every 10 ×σ. The synthesized beam is shown in the right bottom corner of both plots. Labels are given to each of the main components identified in the optical image, which are discussed in Sect. 8.