Variance-weighted stacked residuals obtained after subtracting the best-fit single component Gaussian function to each [CII] spectrum. Red bins represent the residuals within ±800 km s⁻¹, whereas the blue bins mark the spectral region used for estimating the noise. The dotted horizontal line sets the zero level, while the shaded area represents the noise at ±1σ. An ∼3σ excess is visible at velocities ±400 km s⁻¹, suggesting that a further Gaussian component is needed to model the [CII] emission in our galaxies.