The pattern speed of the bar in NGC 4596

Abstract

The pattern speed is a defining parameter of any barred galaxy. A large number of model-dependent techniques have therefore been developed to derive the pattern speed. However, the only model-independent technique for measuring this quantity - the Tremaine-Weinberg method - has hitherto been applied to just one case, the SBO galaxy NGC 936. In this paper, we apply the technique to a second system, the SBa galaxy NGC 4596. The resulting estimate for the pattern speed is Ωp = 52 ± 13 km s-1 kpc-1. This result is corroborated by a spectrum obtained along the major axis of the bar in this system. The corotation radius associated with this pattern speed lies just beyond the end of the bar indicating a fast bar. Combining the bar major-axis spectra with data obtained from a Hubble Space Telescope WFPC2 image, we also find strong evidence for a nuclear disc.