Gaia and the disturbed Milky Way

Paul McMillan (Lund Observatory) - hybrid seminar (in-person in Salle NEF + remote via Zoom)

Abstract:

ESA's Gaia spacecraft has been mapping the Milky Way for almost 10 years, and has changed the way we understand our own galaxy. One of the most striking things that we have learned about the Milky Way 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. 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. 

In this talk I will focus primarily on the outer Milky Way disc, and show how this disturbance can be seen here.  There is a split 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.