Schematic representation of the procedure used to estimate contamination in velocity space. The figure highlights the central voxel (blue) centered on the bulk velocity of stream members, where their density (black dots) is maximal. Background sources (gray points) are distributed more broadly across velocity space. This spatial separation in UVW velocity space enables the estimation of the expected background density at the stream signal location, which is used to calculate each stream’s S/N. The red concentric circles illustrate the neighborhoods across which the expected background number density is estimated.