The radial variation of the LMC-induced reflex motion of the Milky Way disc observed in the stellar halo
arxiv(2024)
摘要
We measure the kinematic signature arising from the Milky Way (MW) disc
moving with respect to the outer stellar halo, which is observed as a dipole
signal in the kinematics of stellar halo tracers. We quantify how the reflex
motion varies as a function of Galactocentric distance, finding that (i) the
amplitude of the dipole signal increases as a function of radius, and (ii) the
direction moves across the sky. We compare the reflex motion signal against a
compilation of published models that follow the MW–LMC interaction. These
models show a similar trend of increasing amplitude of the reflex motion as a
function of distance, but they do not reproduce the direction of the disc
motion with respect to the stellar halo well. We also report mean motions for
the stellar halo as a function of distance, finding radial compression in the
outer halo and nonzero prograde rotation at all radii. The observed compression
signal is also present in MW–LMC models, but the rotation is not, which
suggests that the latter is not induced by the LMC. We extensively validate our
technique to measure reflex motion against idealised tests. We discuss
prospects for directly constraining the mass and orbital history of the LMC
through the impact on the motion of the MW stellar disc, and how the modelling
of the reflex motion can be improved as more and better data become available.
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