The M31–M33 Interaction: Impact on M31’s Center-of-mass Motion and Satellite Orbits

Abstract Inspired by recent studies of the interaction between the Milky Way and the Large Magellanic Cloud and its implications for the Milky Way’s global dynamical history, we investigate how the massive satellite galaxy M33 influences the position and velocity of Andromeda’s (M31) center of mass (COM) as M33 passes through M31’s halo. Using recent six-dimensional phase space measurements for both galaxies, we use backward integration to revisit M33’s orbital history in a massive M31 potential (3 × 10 12 M ⊙ ) for the first time. As previously concluded, we find that a first infall orbit is still the most statistically significant (≳90%) orbital solution for M33, except for a high-mass M31 combined with M31 proper motions from the Hubble Space Telescope (as opposed to Gaia), where there is a greater likelihood (∼65%) of a previous encounter. However, the minimum distance between M33 and M31 during this passage is typically ≥100 kpc, two to three times larger than the distance required to explain M33’s warped stellar and gaseous disks. We quantify the magnitude and direction of M31’s evolving COM position ( R COM ) and velocity ( V COM ) owing to M33, finding R COM ≈ 100–150 kpc at maximum and V COM ≈ 20–40 km s −1 . Furthermore, we explore the implications of this phenomenon for the M31 satellite system, specifically whether M33’s gravitational influence is linked to the lopsided distribution of M31 satellites and whether M33 significantly perturbs the orbits of other M31 satellites. While M33 alone may not explain the lopsided nature of M31’s satellite system, its dynamical impact is nonnegligible and must be accounted for in future dynamical studies of the M31 system.