Distributions of velocity dispersions and rotation curve semi-amplitudes of LEWIS sample. Left panel: Distributions of σ_eff of UDGs from literature (green histogram) and the LEWIS sample. The light blue histogram corresponds to the distribution of galaxies with a constrained fit (C-fit type). Right panel: Distribution of ΔV of UDGs in the LEWIS sample. The pink and blue histograms correspond to UDGs with a mild rotation along any axis (R and IR type) and those without rotation (NR type), respectively.