Absorption properties of the MC at the reference snapshot. UV optical depth (τ_UV at 1600 Å , left y axis) and IR optical depth (τ_IR, at 100 µm , right y axis) as a function of the cloud radius (r). The optical depths are computed along radial lines of sight from the center of the cloud, as is described in Sect. 3.2. The solid blue line gives the median value over 100 lines of sight, while the shaded region indicates the variance (16th–84th percentiles). The shape of the profiles of the UV and IR optical depths computed from the dust distribution is the same and the two profiles are simply re-scaled due to the different dust opacities in the two regimes: τ_UV/τ_IR = κ_{1600 Å}/κ_{100 µm} ≈ 2000. The shaded light blue area brackets the values of the effective optical depth for the six detectors’ observing directions, obtained as $F_{\lambda }=F_{\lambda ,0}{e}^{-{\tau }_{\lambda ,e\text{eff}}}$, where F_λ is the detected flux and F_λ,0 the flux that would be received without dust. We also plot with a dashed line the values of τ_eff for each detector’s observing direction. As a reference, we plot the corresponding optical depth profiles for the S20 model in the homogeneous case (green line) and in the radiation–pressure case (magenta line). The vertical dashed lines show the radius at which the optical depth reaches 90% of the total value in each model.