Constraints from dynamical friction on the dark matter content of barred galaxies

We show that bars in galaxy models having halos of moderate density and a v ariety of velocity distributions all experience a strong drag from dynamica l friction unless the halo has large angular momentum in the same sense as the disk. The frictional drag decreases the bar pattern speed, driving the corotation point out to distances well in excess of those estimated in barr ed galaxies. The halo angular momentum required to avoid strong braking is unrealistically large, even when rotation is confined to the inner halo onl y. We conclude, therefore, that bars are able to maintain their observed hi gh pattern speeds only if the halo has a central density low enough for the disk to provide most of the central attraction in the inner galaxy. We pre sent evidence that this conclusion holds for all bright galaxies.