Figure 9

Figure 9: The dynamical acceleration ap = Vp2∕Rp in units of a0 plotted against the characteristic baryonic surface density [275]. Points as per Figure 5. The dotted line shows the relation ap = GΣb that would be obtained if the visible baryons sufficed to explain the observed velocities in Newtonian dynamics. Though the data do not follow this line, they do show a correlation (1∕2 ap ∝ Σ b). This clearly indicates a dynamical role for the baryons, in contradiction to the simplest interpretation [109] of Figure 5 that dark matter completely dominates the dynamics.