Streamline-based selection of streams. For the VELA 7 galaxy at a redshift z = 1.5, the figure displays path lines for a randomly selected subset of cold gas cells within the galactic disk traced backward over an average disk dynamical time scale, defined as t_trace = R_d/⟨V_rot⟩ and projected onto the x–y plane. These path lines are shown separately for streams (left panel) and non-streams (right panel). To enhance visual clarity, only a portion of the cold gas cells within the disk are included. The path lines are color coded by ±d, where d represents the distance a gas cell has traveled during t_trace, normalized by R_d. Positive values of d indicate inward motion (i.e., the 3D radius at t − t_trace is larger than at the present time), while negative values signify outward movement. Red dashed circles mark the radial boundary of the disk. A threshold value of d_cut = +0.1R_d is used to distinguish inflowing streams from non-streaming gas. Most stream-classified cells (left panel) cluster into two spatially coherent inflowing structures, both showing large positive d values and entering the disk either from the top or bottom-right regions of the projection. In contrast, cells labeled as non-streams (right panel) either show minimal displacement over t_trace (d ≈ 0) or exhibit outward motion with significantly negative d values.