Pattern Corotation Radii from Potential-Density Phase-Shifts for 153 OSUBGS Sample Galaxies

Abstract

We apply the potential-density phase-shift method to 153 galaxies in the Ohio State University Bright Galaxy Survey (OSUBGS) to study the general relationship between pattern corotation radii and the morphology of spiral galaxies. The analysis is based on deprojected near-infrared H-band images. We find that multiple pattern speeds are common in disk galaxies. By selecting those corotation radii close to or slightly larger than the bar radius as being the bar corotation (CR) radius, we find that the average and standard deviation of the ratio R = r(CR)/r(bar), is 1.20+/-0.52 for 101 galaxies having well-defined bars. There is an indication that this ratio depends weakly on galaxy type in the sense that the average ranges from 1.03+/-0.37 for 65 galaxies of type Sbc and earlier, to 1.50+/-0.63 for 36 galaxies of type Sc and later. Our bar corotation radii are on average smaller than those estimated from single-pattern-speed numerical simulations, most likely because these simulations tend to find the pattern speed which generates a density response in the gas that best matches the morphology of the outer spiral structure. Although we find CR radii in most of the sample galaxies that satisfy conventional ideas about the extent of bars, we also consider the alternative interpretation that in many cases the bar CR is actually inside the bar and that the bar ends close to its outer Lindblad resonance instead of its CR. We see evidence in the phase-shift distributions for ongoing decoupling of patterns. We also examine how uncertainties in the orientation parameters of galaxies and in the shapes of bulges affect our results.