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The clustering of orbital poles in the Milky Way’s halo induced by the Large Magellanic Cloud

Presentation #402.04 in the session “How Gaia Reveals the Galaxy’s Secrets: Results on the Galactic Scale, Part 2”.

Published onJun 01, 2021
The clustering of orbital poles in the Milky Way’s halo induced by the Large Magellanic Cloud

Coherence in the phase-space properties of satellite galaxies is a key signature of the Plane of Satellites that exists about our Galaxy. In this talk, I will present tailored N-body simulations of a Milky Way (MW) halo that recently captured a massive (1×1011 Msun) LMC satellite to identify the physical mechanisms that may drive the clustering of orbital poles of objects in orbit about our MW. By tracking the evolution of orbital poles for initially random, steady-state dark matter particles, we find that, after the infall of the LMC, the present-day orbital poles of particles in the simulated MW’s halo are no longer random. Instead, the orbital poles of particles at Galactocentric distances between 50kpc-Rvir cluster near the present-day orbital pole of the LMC and along a sinusoidal pattern across the sky at larger distances. This clustering can be up to a factor of ~1.3 times higher than the density of orbital poles in an isolated MW halo and is most pronounced after the recent, close (~50 Myr ago, 49 kpc) passage of the LMC. The clustering occurs because of two effects: 1) the LMC shifts both the velocity and position of the central density of the MW’s halo and disk. Given our location within the disk, particles in the simulation are observed from a non-inertial reference frame relative to the outer halo leading to an apparent alignment in their orbital poles. 2) The dark matter wake of induced by the LMC changes the kinematics of particles in the Southern Hemisphere. Observations of satellites selected within spatial planes also suffer from a bias, such that measuring orbital poles in a great circle in the sky enhances the probability of their orbital poles being clustered. We expect this scenario to be ubiquitous among hosts that have captured a massive satellite (at least ~1:10 mass ratio) making a recent (< 1 Gyr) pericentric approach, where the massive satellite will cluster orbital poles of halo tracers.

Also presented as abstract #404.03.

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