All-Sky Dynamical Response of the Galactic Halo to the Large Magellanic Cloud

TL;DR

This paper detects the gravitational wake caused by the Large Magellanic Cloud in the Milky Way's halo, revealing disequilibrium and providing insights into the LMC's orbit, galaxy mass, and dark matter properties.

Contribution

First detection of the LMC-induced dynamical wake in the Milky Way halo using all-sky star data, confirming theoretical predictions and indicating a non-equilibrium outer halo.

Findings

Detection of local wake and northern over-density consistent with simulations

Wake location aligns with LMC orbit, supporting first infall scenario

Outer halo is not in dynamical equilibrium

Abstract

Gravitational interactions between the Large Magellanic Cloud (LMC) and the stellar and dark matter halo of the Milky Way are expected to give rise to disequilibrium phenomena in the outer Milky Way. A local wake is predicted to trail the orbit of the LMC, while a large-scale over-density is predicted to exist across a large area of the northern Galactic hemisphere. Here we present the detection of both the local wake and Northern over-density (hereafter the "collective response") in an all-sky star map of the Galaxy based on 1301 stars at 60<R_gal<100 kpc. The location of the wake is in good agreement with an N-body simulation that includes the dynamical effect of the LMC on the Milky Way halo. The density contrast of the wake and collective response are both stronger in the data than in the simulation. The detection of a strong local wake is independent evidence that the Magellanic Clouds are on their first orbit around the Milky Way. The wake traces the path of the LMC, which will provide insight into the orbit of the LMC, which in turn is a sensitive probe of the mass of the LMC and the Milky Way. These data demonstrate that the outer halo is not in dynamical equilibrium, as is often assumed. The morphology and strength of the wake could be used to test the nature of dark matter and gravity.