Left: Relative Mg II absorption velocities to the galaxy systematic redshifts as a function of inferred dark matter halo mass; colour-coded with W₂₇₉₆. The line-of-sight projected halo escape velocities at distances 10 and 30 kpc, assuming an NFW profile of dark matter halos, are marked as dashed and dash-dotted curves. Right: Area-normalized histogram of relative velocity of Mg II absorbers in star-forming galaxies for three mass bins of log(M_★/M_⊙ ≤ 9.5 (hatched at 45°), 9.5 ≤ log(M_★/M_⊙)≤10.2 (hatched at −45°), and log(M_★/M_⊙ ≥ 10.2 (filled histogram). The Gaussian profile for the high-mass bin (solid curve) shows a higher velocity dispersion with σ = 97 km s⁻¹ than σ = 73 km s⁻¹, σ = 87 km s⁻¹ for the respective low-mass bins of log(M_★/M_⊙)≤9.5 (dashed curve), and 9.5 ≤ log(M_★/M_⊙)≤10.2 (dotted curve).