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

Abstract

We show that bars in galaxy models having halos of moderate density and a variety of velocity dis- tributions all experience a strong drag from dynamical friction unless the halo has large angular momen- tum 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 barred galaxies. The halo angular momentum required to avoid strong braking is unrealistically large, even when rotation is conÐned to the inner halo only. We conclude, therefore, that bars are able to maintain their observed high 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 present evidence that this conclusion holds for all bright galaxies.