Global Spiral Arms Formation by Non-linear Interaction of Wakelets
  The formation and evolution of galactic spiral arms is not yet clearly
understood despite many analytic and numerical work. Recently, a new idea has
been proposed that local density enhancements (waklets) arising in the galactic
disk connect with each other and make global spiral arms. However, the
understanding of this mechanism is not yet sufficient. We analyze the
interaction of wakelets by using N-body simulations including perturbing point
masses, which are heavier than individual N-body particles and act as the seeds
for wakelets. Our simulation facilitates more straightforward interpretation of
numerical results than previous work by putting a certain number of perturbers
in a well-motivated configuration. We detected a clear sign of non-linear
interaction between wakelets, which make global spiral arms by connecting two
adjacent wakelets. We found that the wave number of the strongest non-linear
interaction depends on galactic disk mass and shear rate. This dependence is
consistent with the prediction of swing amplification mechanism and other
previous results. Our results provide unification of previous results which
seemed not consistent with each other.
