Amanda Byström (University of Edinburgh): The DESI BHB view of the LMC-halo interaction

Thursday 22 Feb 2024, 14:00 → 15:00 Europe/Stockholm

Title: The DESI BHB view of the LMC-halo interaction
Speaker: Amanda Byström
Affiliation: University of Edinburgh
Time: Thursday 22th February 2024, 1400 to 1500
Location: 90103 Å

 

Abstract: The Large Magellanic Cloud (LMC) is the most luminous and massive Milky Way (MW) satellite. Due to its large mass, the LMC gravitationally attracts the centre of the MW where dynamical timescales are short, moving the inner MW downwards towards the LMC. The outer halo, however, stays fixed. Since we are situated in the MW disc, to us this will look like the outer halo is approaching in the Southern hemisphere and receding in the Northern hemisphere. We thus expect to find a bulk motion of the outer halo that is negative in the South and positive in the North, which increases in strength with distance. In this work, blue horizontal branch (BHB) stars with radial velocities from DESI spectra and accurate distances are used to investigate radial velocity gradients in the outer halo as a function of Galactic latitude and Galactocentric distance. The data set is the biggest set of BHB stars past 50 kpc with radial velocities in literature. We measure an outer halo bulk velocity in the North that is clearly distinct from the one in the South, and which increases in strength with distance. This presents as a dipole in radial velocities on the sky. This proves that the effect of the LMC on the MW is strong, which should be taken into consideration when studying the outer halo.