{\bf Left} The average $^{12}$CO line profile in green and the Gaussian fit to the center of the line in orange. The velocities between the dashed lines are the velocities (and their corresponding flux densities) used in the Gaussian fit. {\bf Right} The residual of the $^{12}CO$ line over the Gaussian fit in green, and the same fit in orange. The dashed lines show peaks of the residual (green) and the fit (orange).