Presentation #227.02D in the session “The Milky Way, The Galactic Center 3”.
Gaia Data Release 2 has enabled the study of local Galactic structure in unprecedented detail. In this talk, I outline an axial symmetry test of our Galaxy’s star counts which is able to pick out certain Galactic structures and trends against the Milky Way’s expected axisymmetric background. Additionally, I will detail some applications of this test and the results achieved to date. Namely, we have used this test of axial symmetry to resolve the most likely sources of axial symmetry-breaking, to demonstrate the existence of non-steady-state effects, to discriminate between various models of the Galaxy’s dark matter halo, and to determine the radius of the Outer Lindblad Resonance (OLR) of the Galactic bar by leveraging the non-axisymmetric nature of bar-resonant orbits. Finally, I will describe how we have used this determination of the OLR radius to infer the pattern speed of the Galactic bar, while avoiding the need to assume a form for the Galactic potential or to directly measure orbits of stars in the dense and dusty Galactic center region. We find a pattern speed of Ωp=49.3±2.2 km s-1 kpc-1, implying that the bar is short and fast.