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 avariety of velocity distributions all experience a strong drag from dynamicalfriction unless the halo has large angular momentum in the same sense as thedisk. The frictional drag decreases the bar pattern speed, driving thecorotation point out to distances well in excess of those estimated in barredgalaxies. The halo angular momentum required to avoid strong braking isunrealistically large, even when rotation is confined to the inner halo only.We conclude, therefore, that bars are able to maintain their observed highpattern speeds only if the halo has a central density low enough for the diskto provide most of the central attraction in the inner galaxy. We presentevidence that this conclusion holds for all bright galaxies.Comment: 46 pages, 18 figures, to appear in ApJ. Uses aaspp4.st