Stellar Motions in the Polar Ring Galaxy NGC 4650A

Abstract

We present the first measurement of the stellar kinematics in the polar ring of NGC 4650A. There is well-defined rotation, with the stars and gas rotating in the same direction, and with similar amplitude. The gaseous and stellar kinematics suggest an approximately flat rotation curve, providing further support for the hypothesis that the polar material resides in a disk rather than in a ring. The kinematics of the emission-line gas at and near the center of the S0 galaxy suggest that the polar disk lacks a central hole. We have not detected evidence of two equal-mass, counterrotating stellar polar streams, as is predicted in the resonance levitation model proposed by Tremaine & Yu. A merger seems the most likely explanation for the structure and kinematics of NGC 4650A.