Stacking H I spectra for the 18 bins. The top, middle, and bottom panels are the stacking results for low-, medium-, and high-mass bins, respectively. The R/R₂₀₀ for each column is denoted on top of the panels. The stacked H I spectra do not show a double-horn profile, but are single-peaked or top-flatted. So we fit the H I flux with a Gaussian function and obtain the H I mass by Gaussian fitting. The shaded regions represent 1σ noise of each spectrum.