Distribution of the line-of-sight velocity difference (Δv) between central galaxies and their satellite candidates. The solid lines with error bars show the PDF of Δv. The dashed lines show the Gaussian-plus-a-constant fits to the data points. The error bars correspond to the standard deviation of 100 bootstrap samples. The upper row shows the results for star-forming centrals, while the lower row is for the total central population. The results of the star-forming and total samples in different stellar mass bins are shown in different columns. We note that the scales of the vertical axes are different for different panels.