The Contribution of Spiral Arms to the Thick Disk along the Hubble
  Sequence
  The first mechanism invoked to explain the existence of the thick disk in the
Milky Way Galaxy, were the spiral arms. Up-to-date work summon several other
possibilities that together seem to better explain this component of our
Galaxy. All these processes must affect differently in distinct types of
galaxies, but the contribution of each one has not been straightforward to
quantify. In this work, we present a first comprehensive study of the effect of
the spiral arms in the formation of thick disks, as going from early to late
type disk galaxies, in an attempt to characterize and quantify this specific
mechanism in galactic potentials. To this purpose, we perform numerical
simulations of test particles in a three-dimensional spiral galaxy potential of
normal spiral galaxies (from early to late types). By varying the parameters of
the spiral arms we found that the vertical heating of the stellar disk becomes
very important in some cases, and strongly depends on the galaxy morphology,
pitch angle, arms mass and its pattern speed. The later the galaxy type, the
larger is the effect on the disk heating. This study shows that the physical
mechanism causing the vertical heating is different from simple resonant
excitation. The spiral pattern induce chaotic behavior not linked necessarily
to resonances but to direct scattering of disk stars, which leads to an
increase of the velocity dispersion. We applied this study to the specific
example of the Milky Way Galaxy, for which we have also added an experiment
that includes the Galactic bar. From this study we deduce that the effect of
spiral arms of a Milky-Way-like potential, on the dynamical vertical heating of
the disk is negligible, unlike later galactic potentials for disks.
