BARS DO DRIVE SPIRAL DENSITY WAVES

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(b), maximum spiral strengths Q(s), and maximum m = 2 arm contrasts A(2s) for 23 galaxies with deep Anglo-Australian Telescope (AAT) K(s)-band images. These were combined with previously published Q(b) and Q(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(b) and Q(s) was confirmed for the combined sample, whereas the AAT subset alone showed no significant correlations between Q(b) and Q(s), nor between Q(b) and A(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 approximate to 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 approximate to 1.4 bar radii. Our new results confirm that, at least in a statistical sense, bars do indeed drive spiral density waves.