Histogram is the probability density function (pdf) of line centroid velocity fluctuations between neighboring positions over the whole NH₃ map of the filament L1251A except for the outlier at the offset (Δα,Δδ) = ( − 200′′, −40′′). In the upper left hand corner, the grid with color points illustrates the calculation of ΔV_i,j: for a current position (i,j) (marked by red), the velocity differences are calculated between each blue point and the central red point. The total number of different pairs is 680. The histogram is approximated by a Gauss (black) and a Lorentz (red) function with the widths (FWHP) of Δv_G = 0.22 km s^-1 and Δv_L = 0.11 km s^-1.