DYNAMICAL FRICTION AND THE DISTRIBUTION OF DARK-MATTER IN BARRED GALAXIES

We use fully self-consistent N-body simulations of barred galaxies to show that dynamical friction from a dense dark matter halo dramaticall y slows the rotation rate of bars. Our result supports previous theore tical predictions for a bar rotating within a massive halo. On the oth er hand, low-density halos, such as those required for maximum disks, allow the bar to continue to rotate at a high rate. There is somewhat meager observational evidence indicating that bars in real galaxies do rotate rapidly, and we use our result to argue that dark matter halos must have a low central density in all high surface brightness disk g alaxies, including the Milky Way. Bars in galaxies that have larger fr actions of dark matter should rotate slowly, and we suggest that a pro mising place to look for such candidate objects is among galaxies of i ntermediate surface brightness.