Bars do drive spiral density waves
  Recently, Buta etal. (2009) examined the question "Do Bars Drive Spiral
Density Waves?", an idea supported by theoretical studies and also from a
preliminary observational analysis Block etal (2004). 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 AAT K_s-band images. These were combined with
previously published Q_b and Q_s values for 147 galaxies from the OSUBSGS
sample and with the 12 galaxies from Block etal(2004). 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 etal. (2009) 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 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 we find a significant correlation between local
parameters out to 1.4 bar radii. Our new results confirm that, at least in a
statistical sense, bars do indeed drive spiral density waves.
