Seminarium: Agreeing on the elephant: Milky Way dynamics in the Gaia era

One of the most striking things that we have learned about the Milky Way from Gaia data is the extent to which it is disturbed. The way we describe and characterise this disturbance seems to depend on how we are looking at it, much like a blindfolded scientist studying an elephant by touch alone. We can at least agree that the Milky Way’s disc is rippling up and down, and the prime suspect for this disturbance is the Sagittarius dwarf galaxy shaking the disc as it passed by some time ago. This has been best studied in the solar neighbourhood, where a clear ’phase spiral’ has been observed: a strong dependence of typical rotational velocity around the galactic centre as a function of a stars height above the plane and vertical velocity. In this talk I will focus more on the outer Milky Way disc, and show that a disturbance can be seen here too. This is a bifurcation of the velocity distribution into two clumps: one rotating slower around the galactic centre and moving downwards, and one rotating faster and moving upwards. I will show that this is also produced in simulations of the impact of the Sagittarius dwarf on the Milky Way disc, and argue that these disturbances will allow us to conduct ’Galactic-seismology’ and determine the structure and history of the Milky Way with new clarity.

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We shall leave for lunch at around 12:15. There will be fika after the seminar.