The formation of a thick disk through the heating of a thin disk:
  Agreement with orbital eccentricities of stars in the solar neighborhood
  We study the distribution of orbital eccentricities of stars in thick disks
generated by the heating of a pre-existing thin stellar disk through a minor
merger (mass ratio 1:10), using N-body/SPH numerical simulations of
interactions that span a range of gas fractions in the primary disk and initial
orbital configurations. The resulting eccentricity distributions have an
approximately triangular shape, with a peak at 0.2-0.35, and a relatively
smooth decline towards higher values. Stars originally in the satellite galaxy
tend to have higher eccentricities (on average from e = 0.45 to e = 0.75),
which is in general agreement with the models of Sales and collaborators,
although in detail we find fewer stars with extreme values and no evidence of
their secondary peak around e = 0.8. The absence of this high-eccentricity
feature results in a distribution that qualitatively matches the observations.
Moreover, the increase in the orbital eccentricities of stars in the solar
neighborhood with vertical distance from the Galactic mid-plane recently found
by Diericxk and collaborators can be qualitatively reproduced by our models,
but only if the satellite is accreted onto a direct orbit. We thus speculate
that if minor mergers were the dominant means of formating the Milky Way thick
disk, the primary mechanism should be merging with satellite(s) on direct
orbits.
