Relative velocity distribution of 6349 Mg II NALs with z_em < 1.07. The data are directly taken from the 17 316 Mg II NALs of Chen et al. (2018a). The red dashed, blue dashed, and blue solid curves indicate the Gaussian function fits corresponding to inflow, environment, and outflow Mg II NALs, respectively. The green solid line indicates the mean count at υ_r > 6000 km s⁻¹, which corresponds to intervening Mg II NALs. The red solid curve is the sum of all the colored lines. The values shown in the top right corner are the Gaussian function fitting centers (υ₀) and dispersions (σ).