The dark halo of the polar-ring galaxy NGC 4650A

By analyzing the rotation of its central disk and outer polar ring, we place limits on the flattening of the unseen halo of the galaxy NGC 4650A. We fit a model consisting of a bulge, disk, axisymmetric dark halo, and massive polar ring to both rotation curves and show that the observations are consistent with a range of halo flattening, from spherical to as flat as an E8 elliptical galaxy. The best fits are obtained for dark halo flattenings in the range E3-E7. The substantial mass of the ring is probably responsible for a characteristic "wiggle" in the polar rotation curve; fits to this feature suggest that there may be considerably more mass in the ring than has been reported from neutral hydrogen measurements.