The long-term stability of the Vast Polar Structure and its connection to a possible previous passage of the LMC

TL;DR

This study demonstrates that the Vast Polar Structure of dwarf galaxies around the Milky Way has remained stable over 5 billion years, indicating it predates the LMC's recent infall and is only mildly affected by it.

Contribution

It provides the first long-term dynamical analysis showing the VPOS's stability and its connection to the LMC's orbital history over 5 Gyr.

Findings

VPOS has remained stable in thickness and orientation over 5 Gyr.

LMC's gravitational influence causes only mild perturbations to VPOS.

The VPOS likely originated from satellites stripped during the LMC's first passage.

Abstract

The Vast Polar Structure (VPOS) is a thin, planar arrangement of co-orbiting dwarf galaxies, nearly perpendicular to the Milky Way (MW) disc. In this work we investigate the persistence and stability of the VPOS over time. We identify VPOS member galaxies and integrate their orbits over the past 5 Gyr using time evolving gravitational potentials that account for the mutual interaction between the MW and the Large Magellanic Cloud (LMC). The reconstructed trajectories allow us to examine the long-term evolution of the VPOS. We identify 15 galaxies as members of the VPOS, including 9 MW and 6 LMC satellites. We find that the VPOS has remained a stable structure, maintaining a roughly constant thickness ($\sim$ 15 kpc), flattening ($c/a \sim$ 0.2), and orientation over time. While the LMC exerts a strong gravitational influence on the MW satellites, its impact on the VPOS is limited, leading only to mild perturbations. The structural properties of the VPOS remain almost unchanged, whether or not LMC satellites are included in the analysis, indicating a smooth dynamical integration with the rest of VPOS members upon entering the MW virial radius. This minimal dynamical impact on the VPOS results from the remarkable alignment between the LMC's orbit and the plane's orientation. We conclude that the VPOS is a stable, long-lived structure that predates the recent infall of the LMC and retains nearly constant structural properties over the last 5 Gyrs. Our findings suggest a strong connection between the VPOS and the LMC, consistent with a scenario in which the LMC is on its second pericentre and the VPOS originated primarily from satellites stripped during the first passage.