The Secular Evolution of Disk Structural Parameters
- Additional Document Info
- View All
We present a comprehensive series of $N$-body as well as $N$-body + SPH
simulations to study the secular evolution of the structure of disk galaxies.
Our simulations are organized in a hierarchy of increasing complexity, ranging
from rigid-halo collisionless simulations to fully live simulations with gas
and star formation. Comparisons between the different types of simulations
allow us to isolate the role of various physical mechanisms. We focus on the
evolution of systems expected in a LCDM universe.
Our goal is to examine which structural properties of disk galaxies may
result from secular evolution rather than from direct hierarchical assembly. In
the vertical direction, we find that various mechanisms can lead to heating.
The strongest heating occurs during the vertical buckling instability of a bar.
Among the consequences of this instability is the formation of peanut-shaped
bulges which produce clear kinematic signatures when observed face-on. We find
that bars are robust structures that are not destroyed by buckling. They can be
destroyed instead by a central mass concentration but we find that this mass
needs to be a large fraction of the total mass of the disk. We then study the
evolution of stellar surface density profiles showing how angular momentum
redistribution leads to increasing central densities and disk scale lengths and
to profile breaks at large radii. The breaks in these simulations are in
excellent agreement with observed breaks, even when the evolution is purely
collisionless. Disk scale-lengths increase even when the total disk angular
momentum is conserved; thus mapping halo angular momenta to scale-lengths is
has subject area