A fast bar in the post-interaction galaxy NGC 1023

We measured the bar pattern speed, Ω_p, of the SB0 galaxy NGC 1023 using the Tremaine-Weinberg method with stellar-absorption slit spectroscopy. The morphology and kinematics of the HI gas outside NGC 1023 suggest it suffered a tidal interaction, sometime in the past, with one of its dwarf companions. At present, however, the optical disc is relaxed. If the disc had been stabilized by a massive dark matter halo and formed its bar in the interaction, then the bar would have to be slow. We found Ω_p =5.0+/-1.8 km/s/arcsec, so that the bar ends near its corotation radius. It is therefore rotating rapidly and must have a maximum disc.