Comparison of the luminosity of the simulated subhaloes and the observational limits set for the two detections. First, we selected the systems that best match the observational inference in terms of projected slope and enclosed mass: in practice, these were selected within the orange rectangles in the top panels of Fig. 8. We computed their luminosity, L_V, from the V-band magnitudes provided in the TNG50-1 subhalo catalogue and plot them as orange circles as a function of the subhalo mass, M_sub. We show the results for B1938+666 on the left and J0946+1006 on the right. The black dots show instead the luminosity of the general subhalo population at the same redshift. The observational upper limits (see Sect. 3) are represented by the horizontal red line in the plot.