Top row: density of stars in ϕ₂ (gray) and inferred density (black curve) for regions around the spur, blob, and a control field. The model for the density includes components for the stream, background, and a feature overdensity (the spur or the blob), but with amplitudes that are allowed to go to zero (see Section 3.2 for more details.) Bottom row: inferred posterior probability distributions over the amplitude (α) of each component in each field: α_s for the stream, α_bg for the background, and α_f for the feature. In both feature fields, the model prefers an additional component to describe the feature, whereas in the control field the density is consistent with stream + background.