One realisation of a uni-dimensional turbulent velocity field (middle panel) along the spatial axis x (in arbitrary units) with parameters α = 1/3, k_min = 1 (L_inj = 2), k_max = 20 (L_diss = 0.1), σ_turb = 160 km s⁻¹, and σ_th = 100 km s⁻¹ (shown by yellow shading). The emissivity profile (top panel) of the gas corresponds to a β density model with core radius r_c = 0.2 and at a distance θ = 0.2 from the centre. The lower panel shows the resulting line profile as a thick black line. The best-fit Gaussian centred on C (vertical line) of width S is shown as a dashed red line. The green thin curve shows the Gaussian centred on the line centroid. Its width equals the geometrical mean of the thermal and turbulent broadening.