Figure 22

Figure 22: The rotation curve [124] and MOND fit [384] of the Local Group spiral M33 assuming a constant stellar mass-to-light ratio (top panel). While the overall shape is a good match, there is a slight mismatch at ∼ 3 kpc and above 7 kpc. The observed color gradient implies a slight variation in the mass-to-light ratio, in the sense that the stars at small radii are slightly redder and heavier than those at large radii. Applying stellar population models [42] to the observed color gradient produces a slight adjustment of the Newtonian mass model. The dotted line in the lower panel reiterates the constant M ∕L model from the top panel, while the solid line has been corrected for the observed color gradient. This slight adjustment to the baryonic mass distribution considerably improves the fit.