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Paper: Multiple Pattern Speeds in Disc Galaxies
Volume: 486, Multi-Spin Galaxies
Page: 133
Authors: Font, J.; Querejeta, M.; Beckman, J. E.; James, P.
Abstract: We have used 2-dimensional velocity maps derived from Fabry-Perot data cubes, mapping the Hα emission line from gas-rich nearby galaxies, to determine the resonance radii. This is done by subtracting off the rotation curve model from the initial velocity map yielding the residual velocity field, and finding the galactocentric radii at which these residual velocities change phase in the radial direction. A histogram of the number of pixels across which the phase changes take place shows a set of well defined peaks which give the resonance radii. We can then use the frequency curves, derived from the rotation curve, to identify which resonances are corotations. Some of these correspond to bars, others to other disk features. We find an interesting pattern in over 70% of the sample: given two pattern speeds, say Ω1 and Ω2, the outer Lindblad resonance of Ω1 coincides with the corotation of Ω2, and the inner 4:1 resonance of Ω2 coincides with the corotation of Ω1. We compute the ratio of corotation radius to bar length where we have good enough image quality, finding a mean value of 1.3, and a shallow increase towards later type galaxies. In double barred galaxies we find that the nuclear bar rotates 3.3–3.6 times faster than the main bar.
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