Zoom-in plots of the HC₃N (left) and N₂H⁺ (right) emission for IRAS 4A, together with the best free-fall trajectory found for the T_MB and υ_LSR maps. Top: amplitude T_MB of the Gaussian components corresponding to HC₃N cluster 6 and to the blue N₂H⁺ cluster. The black polygon marks the region selected as a potential streamer. The white curve marks the potential streamer trajectory. The blue and red arrows indicate the direction of the outflow lobes for IRAS 4A and 4B, and the black arrow on the N₂H⁺ map shows the orientation of the position-velocity diagram at the bottom. Middle: central velocities vLSR of the Gaussian component. A scale bar representing 2000 au is shown in the top right corner of the image. Bottom left: KDE of the υ_LSR within the selected region. The black line at the bottom of the plot represents a length of one beam. The blue curve marks the velocity vs. the distance for the found free-fall solution. The dashed black line represents the protostar υ_LSR. Bottom right: N₂H⁺ position–velocity diagram along the path indicated in the top panel. The dashed horizontal line marks the υ_LSR of the source (6.9 km s⁻¹, Stephens et al. 2019). The black scale bar represents a length equivalent to one beam.