Probability density distributions from our model-fitting for the SiS line of channels 15 and 20, using a Gaussian source model with addition of a delta function model. The vertical dashed lines indicate the estimated best-fit values and their ±3σ deviations. The horizontal dashed line is set to 3 × 10⁻³ (i.e., the probability density corresponding to the 3σ cutoff of a Gaussian probability distribution). The peaks of the PDFs have been further scaled to 1, for clarity.