The Galactic bar’s outer Lindblad resonance (OLR) in Gaia’s action-angle space

The Milky Way’s central bar strongly affects the stellar motions in the Galactic disk. Resonances — especially the outer Lindblad resonance (OLR) — are expected to create ridges in the space of orbital actions. And indeed, Gaia has revealed several such ridges. However, as the bar’s pattern speed is still disputed, also the true OLR — and in fact the dynamical origin of any of these ridges — remains a puzzle. In this talk, I investigate if the orbital phase angles of stars in one of these ridges are consistent with the characteristic shape of OLR orbits. I conclude that the Gaia RVS data favors either the “Hat” or the “Sirius” ridge to be the OLR, and consequently either a bar pattern speed of ~33 km/s/kpc or ~39 km/s/kpc.