Line-of-sight VSFs for the cold component and for the projected radius r ≤ 25 kpc averaged between 0.9 and 4 Gyr. The darkest curve (labeled ℓ_3D) was obtained by taking the three-dimensional distance between pairs of points, similarly to Wang et al. (2021). For all the other curves, the VSFs were computed out of projected maps, and the corresponding separations scales are two dimensional (ℓ_2D). The term w(Hα) indicates weighting of the map by Hα emission, and 𝒮 is the additional smoothing effect resulting from atmospheric seeing (see Li et al. 2020). The shaded areas indicate the time variation of each VSF.