A map of the non-thermal velocity dispersion to the gas sound speed in G035.39. In pixels where multiple velocity components are discovered, the smallest value is shown on the image (the analyses throughout the rest of this work use all the values). The markers are the same as in Fig. 1, and the solid white line contours indicate the transition at σ_nt ∕c_s = 1. The side panels to the left and right of the map show (1,1) and (2,2) spectra towards the numbered positions. The spectra are overlaid with their best-fit model, with individual velocity components plotted in colour. The topmost spectra, unlike the others, show an averaged spectrum across the subsonic island at α(J2000) = 18h57m08s, δ(J2000) = +2∘09′45′′. An independently conducted fit, shown in red, yields ℳ = 0.72 ± 0.04.