Differential velocity distribution of the all spectral members of Cl J0227-0421. The median redshift of the secure members is shown in the top right corner of the plot. Also shown in the top right corner is the value of the best-fit line of sight (LOS) velocity dispersion (σ_v, see Sect. 3.1 for details). The resulting Gaussian function generated by the best-fit σ_v is overplotted on the differential velocity histogram (solid black line) along with those functions generated from σ_v ± σ_σv. The high degree of skewness of the differential velocity distribution of member galaxies can be clearly seen.