Histogram of metallicity gradient distribution of galaxies with or without a regular velocity field. The right panel is for the distribution of residual metallicity gradient after removing the best-fit linear dependence on stellar mass. The gray filled histograms represent galaxies with a clear rotation velocity field, while the black open histograms represent galaxies without a regular gaseous rotational velocity field. The two dotted vertical lines in each panel represent the median values of the two subsamples, and the value in the upper left corner corresponds to the p-value from the Kolmogorov-Smirnov tests conducted between galaxies with or without a regular velocity field.