[C II] spectrum along pv diagram in NGC 1977 (Fig. 17) with Gaussian fits, averaged over 201′′ × 201′′. Coordinate offsets indicate the lower left-hand corner of the square over which the spectrum is averaged. The two narrow components stem from the expanding shell, while the broad component originates in the ionized gas that is contained within the shell. Since the bubble expands in both directions, the peak-velocity difference is twice the expansion velocity, v_exp ≃ 1.3 km s⁻¹. The fit parameters are given in Table 4.