Structure in phase space associated with spiral and bar density waves in
  an N-body galactic disk
  An N-body hybrid simulation, integrating both massive and tracer particles,
of a Galactic disk is used to study the stellar phase space distribution or
velocity distributions in different local neighborhoods. Pattern speeds
identified in Fourier spectrograms suggest that two-armed and three-armed
spiral density waves, a bar and a lopsided motion are coupled in this
simulation, with resonances of one pattern lying near resonances of other
patterns. We construct radial and tangential (uv) velocity distributions from
particles in different local neighborhoods. More than one clump is common in
these local velocity distributions regardless of the position in the disk.
Features in the velocity distribution observed at one galactic radius are also
seen in nearby neighborhoods (at larger and smaller radii) but with shifted
mean v values. This is expected if the v velocity component of a clump sets the
mean orbital galactic radius of its stars. We find that gaps in the velocity
distribution are associated with the radii of kinks or discontinuities in the
spiral arms. These gaps also seem to be associated with Lindblad resonances
with spiral density waves and so denote boundaries between different dominant
patterns in the disk. We discuss implications for interpretations of the Milky
Way disk based on local velocity distributions. Velocity distributions created
from regions just outside the bar's Outer Lindblad resonance and with the bar
oriented at 45 degrees from the Sun-Galactic center line more closely resemble
that seen in the solar neighborhood (triangular in shape at lower uv and with a
Hercules like stream) when there is a strong nearby spiral arm, consistent with
the observed Centaurus Arm tangent, just interior to the solar neighborhood.
