Pattern Speeds of Bars and Spiral Arms From H-alpha Velocity Fields
  We have applied the Tremaine-Weinberg method to 10 late-type barred spiral
galaxies using data cubes, in H-alpha emission, from the GHAFAS and FANTOMM
Fabry-Perot spectrometers. We have combined the derived bar (and/or spiral)
pattern speeds with angular frequency plots to measure the corotation radii for
the bars in these galaxies. We base our results on a combination of this method
with a morphological analysis designed to estimate the corotation radius to
bar-length ratio using two independent techniques on archival near infrared
images, and although we are aware of the limitation of the application of the
Tremaine-Weinberg method using ionised gas observations, we find consistently
excellent agreement between bar and spiral arm parameters derived using
different methods. In general, the corotation radius, measured using the
Tremaine-Weinberg method, is closely related to the bar length, measured
independently from photometry and consistent with previous studies. Our
corotation/bar-length ratios and pattern speed values are in good agreement
with general results from numerical simulations of bars. In systems with
identified secondary bars, we measure higher H-alpha velocity dispersion in the
circumnuclear regions, whereas in all the other galaxies, we detect flat
velocity dispersion profiles. The excellent agreement between the
Tremaine-Weinberg method results and the morphological analysis and bar
parameters in numerical simulations, suggests that although the H-alpha
emitting gas does not obey the continuity equation, it can be used to derive
the bar pattern speed.
