We study geometries of galactic rotation curves from Dark Matter (DM) and Modified Newtonian Dynamics (MOND) models in $(g_{rm bar},g_{rm tot})$-space ($g2$-space) where $g_{rm tot}$ is the total centripetal acceleration of matter in the galaxies and $g_{rm bar}$ is that due to the baryonic (visible) matter assuming Newtonian gravity. The $g2$-space geometries of the models and data from the SPARC database are classified and compared in a rescaled $hat{g}2$-space that reduces systematic uncertainties on galaxy distance, inclination angle and variations in mass to light ratios. We find that MOND modified inertia models, frequently used to fit rotation curve data, are disfavoured at more than 5$sigma$ independent of model details. The Bekenstein-Milgrom formulation of MOND modified gravity compares better with data in the analytic approximation we use. However a quantitative comparison with data is beyond the scope of the paper due to this approximation. NFW DM profiles only agree with a minority of galactic rotation curves. Improved measurements of rotation curves, in particular at radii below the maximum of the total and the baryonic accelerations of the curves are very important in discriminating models aiming to explain the missing mass problem on galactic scales.
Download