The Mass Discrepancy–Acceleration Relation: Disk Mass and the Dark Matter Distribution

The mass discrepancy in disk galaxies is shown to be well correlated withacceleration, increasing systematically with decreasing acceleration below acritical scale a0 = 3700 km^2/s^2/kpc = 1.2E-10 m/s/s. For each galaxy, thereis an optimal choice of stellar mass-to-light ratio which minimizes the scatterin this mass discrepancy-acceleration relation. The same mass-to-light ratiosalso minimize the scatter in the baryonic Tully-Fisher relation and are inexcellent agreement with the expectations of stellar population synthesis. Oncethe disk mass is determined in this fashion, the dark matter distribution isspecified. The circular velocity attributable to the dark matter can beexpressed as a simple equation which depends only on the observed distributionof baryonic mass. It is a challenge to understand how this very fine-tunedcoupling between mass and light comes about.Comment: Accepted for publication in the Astrophysical Journal. 34 pages including 9 figures (AASTeX