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Stellar Dynamics in the Outer Galactic Disk under the Influence of a Central Bar
In this work, we investigate the possible influence of a central bar in a disk galaxy on the velocity distribution in the outer stellar disk, which is thought to arise mostly via resonant phenomena. For this, we numerically integrate orbits of a large number of sample points in a 2D model potential consisting of a rotating bar component in an axisymmetric background. Central to our analysis is the construction of the first and second moments of the velocity distribution in their spatial variability. From these, other important quantities like Oort constants, dispersion axis ratio and vertex deviation can be deduced. For the latter, we predict non-vanishing values for a large number of kinematical configurations. Regarding the axis ratio, we are able to obtain values smaller than 1/2, in agreement with observations in the solar neighbourhood which are hitherto unexplained by theory. All our results are consistent with a proposed position of the Sun lying shortly outside of the co-rotation radius and lagging behind the bar by around 30 degree. We repeat part of our analysis for model potentials including spiral structure, in order to estimate how much our results will be affected by this. It turns out that in many cases our bar-induced features continue to prevail, whereas the extent of the spiral effects is seen to depend particularly on pitch angle, which for the case of the Milky Way is very poorly constrained.
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530 Physik
530 Physics