Speaker
Description
The Large Magellanic Cloud (LMC) is a Milky Way (MW) satellite that is massive enough to gravitationally attract the MW disc and inner halo, causing them to move significantly with respect to the outer halo. In this talk, I will present measurements of this interaction using the first two years of DESI spectroscopic survey observations. We probe this interaction by constructing a sample of almost 10,000 blue horizontal branch (BHB) stars with radial velocities from DESI out to 120 kpc from the Galactic centre. This is the largest spectroscopic set of BHB stars in the literature to date, drastically increasing the number of known BHB stars in the outer halo. Using the DESI BHB sample combined with SDSS BHBs, we observe that the mean velocity in the Southern Galactic hemisphere is different by 3.7$\sigma$ from the North. To understand this, I will demonstrate how we model the (sky-projected) velocity field of the halo, which shows a dipole component that is directed 22 degrees away from the LMC along its orbit, which we interpret as the travel direction of the inner MW. The velocity field includes a monopole term that is $-24$ km/s, which indicates that the outer halo is being compressed. While this work uses DESI data, we expect that upcoming DESI and Gaia data releases providing improved stellar samples with proper motions, will allow us to even better characterise the MW and LMC's interaction.
