Top: histogram containing the number of objects per channel contributing to the stacked flux. Central lower panel: variance-weighted stacked [C II] residuals from a single-Gaussian fit in spectral bins of 25 km s⁻¹ (75 km s⁻¹). The green solid lines at ±800 km s⁻¹ enclose the velocity range excluded for the estimation of spectral noise, while the blue dashed lines represent the spectral rms at ±1σ. Channels in violet represent the channels in the velocity range enclosed by the outermost peaks at ≥3σ in the 75 km s⁻¹-binned stacked residuals. This helps in visualizing the velocity interval affected by flux excesses.