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 .