  The inner parts of many spiral galaxies are dominated by bars. These are
strong non-axisymmetric features which significantly affect orbits of stars and
dark matter particles. One of the main effects is the dynamical resonances
between galactic material and the bar. We detect and characterize these
resonances in N-body models of barred galaxies by measuring angular and radial
frequencies of individual orbits. We found narrow peaks in the distribution of
orbital frequencies with each peak corresponding to a specific resonance. We
found five different resonances in the stellar disk and two in the dark matter.
The corotation resonance and the inner and outer Lindblad resonances are the
most populated. The spatial distributions of particles near resonances are
wide. For example, the inner Lindblad resonance is not localized at a given
radius. Particles near this resonance are mainly distributed along the bar and
span a wide range of radii. On the other hand, particles near the corotation
resonance are distributed in two broad areas around the two stable Lagrange
points. The distribution resembles a wide ring at the corotation radius.
Resonances capture disk and halo material in near-resonant orbits. Our analysis
of orbits in both N-body simulations and in simple analytical models indicates
that resonances tend to prevent the dynamical evolution of this trapped
material. Only if the bar evolves as a whole, resonances drift through the
phase space. In this case particles anchored near resonant orbits track the
resonance shift and evolve. The criteria to ensure a correct resonant behavior
discussed in Weinberg & Katz (2007a) can be achieved with few millions
particles because the regions of trapped orbits near resonances are large and
evolving.
