Orthogonal rotating gaseous disks near the nucleus of NGC 253

Abstract

The central ~150 pc region of the starburst galaxy NGC 253 is shown to have a distinct gaseous kinematic subsystem, exhibiting rotation in a plane perpendicular to the galactic disk, and an interior region with possible counterrotation in the plane of the disk. In addition, solid-body rotation in the same sense as the galactic disk is observed in the outer parts of the central region. We suggest that this kinematic subsystem in NGC 253 may be indicative of a secondary bar inside the known primary bar. Alternatively, it may be a signature of a merger or an accretion event during the history of the galaxy. The dynamical mass within a radius of 5" is ~3 × 10⁸ M_⊙. These results are based on a two-dimensional image of the velocity field of the H92α recombination line in the central 9" × 4" region, with an angular resolution of 1".8 × 1".0, made using observations in the B, C, and D configurations of the VLA.