N-Body Simulations of Collective Effects in Spiral and Barred Galaxies
  We present gravitational N-body simulations of the secular morphological
evolution of disk galaxies induced by density wave modes. In particular, we
address the demands collective effects place on the choice of simulation
parameters, and show that the common practice of the use of a large gravity
softening parameter was responsible for the failure of past simulations to
correctly model the secular evolution process in galaxies, even for those
simulations where the choice of basic state allows an unstable mode to emerge,
a prerequisite for obtaining the coordinated radial mass flow pattern needed
for secular evolution of galaxies along the Hubble sequence. We also
demonstrate that the secular evolution rates measured in our improved
simulations agree to an impressive degree with the corresponding rates
predicted by the recently-advanced theories of dynamically-driven secular
evolution of galaxies. The results of the current work, besides having direct
implications on the cosmological evolution of galaxies, also shed light on the
general question of how irreversibility emerges from a nominally reversible
physical system.
