Stellar Kinematics for the Central Spheroid in the Polar Disk Galaxy NGC 4650A

Abstract

We have obtained high angular resolution, high signal-to-noise ratio spectra of the calcium triplet absorption lines on the photometric axes of the stellar spheroid in the polar disk galaxy NGC 4650A. Along the major axis, the observed rotation and velocity dispersion measurements show the presence of a kinematically decoupled nucleus and a flat velocity dispersion profile. The minor-axis kinematics is determined for the first time: along this direction some rotation is measured, and the velocity dispersion is nearly constant and slightly increases at larger distances from the center. The new high-resolution kinematic data suggest that the stellar component in NGC 4650A resembles a nearly exponential oblate spheroid supported by rotation. The main implications of these results on the previous mass models for NGC 4650A are discussed. Moreover, the new kinematic data set constraints on current models for the formation scenarios of polar ring galaxies, supporting a slow accretion rather than a secondary strong dissipative event.