Panchromatic SED of Andromeda. The black line is the best fitting RT model, run at high resolution (512 wavelengths). The green points are the observed integrated luminosities for M 31. The red, blue and cyan lines represent the SEDs for simulations with only one stellar component: evolved, young and ionising, respectively. The interstellar dust component is still present in these simulations. The bottom panel shows the residuals between the observations and the best fitting (black) model.