On the galaxy spiral arms' nature as revealed by rotation frequencies
  High resolution N-body simulations using different codes and initial
condition techniques reveal two different behaviours for the rotation frequency
of transient spiral arms like structures. Whereas unbarred disks present spiral
arms nearly corotatingwith disk particles, strong barred models (bulged or
bulge-less) quickly develop a bar-spiral structure dominant in density, with a
pattern speed almost constant in radius. As the bar strength decreases the arm
departs from bar rigid rotation and behaves similar to the unbarred case. In
strong barred models we detect in the frequency space other subdominant and
slower modes at large radii, in agreement with previous studies, however we
also detect them in the configuration space. We propose that the distinctive
behaviour of the dominant spiral modes can be exploited in order to constraint
the nature of Galactic spiral arms by the astrometric survey GAIA and by 2-D
spectroscopic surveys like CALIFA and MANGA in external galaxies.
