BARS DO DRIVE SPIRAL DENSITY WAVES

Abstract

Recently, Buta et al. examined the question 'Do Bars Drive Spiral Density Waves?', an idea supported by theoretical studies and also from a preliminary observational analysis. They estimated maximum bar strengths Q{sub b} , maximum spiral strengths Q{sub s} , and maximum m = 2 arm contrasts A {sub 2s} for 23 galaxies with deep Anglo-Australian Telescope (AAT) K{sub s} -band images. These were combined with previously published Q{sub b} and Q{sub s} values for 147 galaxies from the Ohio State University Bright Spiral Galaxy Survey (OSUBSGS) sample and with the 12 galaxies from Block et al. Weak correlation between Q{sub b} and Q{sub s} was confirmed for the combined sample, whereas the AAT subset alone showed no significant correlations between Q{sub b} and Q{sub s} , nor between Q{sub b} and A {sub 2s}. A similar negative result was obtained in Durbala et al. for 46 galaxies. Based on these studies, the answer to the above question remains uncertain. Here we use a novel approach, and show that although the correlation between the maximum bar and spiral parameters is weak, these parameters do correlate when compared locally. For the OSUBSGS sample, a statistically significant correlation is found between the local spiral amplitude, and the forcing due to the bar's potential at the same distance, out to {approx}1.6 bar radii (the typical bar perturbation is then of the order of a few percent). Also for the sample of 23 AAT galaxies of Buta et al., we find a significant correlation between local parameters out to {approx}1.4 bar radii. Our new results confirm that, at least in a statistical sense, bars do indeed drive spiral density waves.