Same as Fig. 7 but with the addition of the predictions from the TNG100 and EAGLE simulations of matched galaxies. Shaded regions give the order of magnitude of the systematic uncertainty due to the process used to create mock observations. Shaded regions are shown for the TNG simulation. For EAGLE, shaded regions should have a similar width, but they are not shown so as to not overcrowd the figure. We show the observed and predicted soft X-ray luminosity from the central 80 kpc (bottom left) from the full 300 kpc (bottom right) and for the 80 <  R_p <  300 kpc range (main top panel) as a function of galaxy stellar mass.