Galactic seismology: can a disc-crossing impulse explain the large-scale perturbations in the Milky Way’s disc?

Abstract The dwarf galaxy Sagittarius (Sgr), once a major satellite galaxy with mass Msgr ~ 1011 M⊙, has been heavily stripped by the Milky Way (MW) over the past 5 − 6 Gyr through multiple disc crossings. Recent models have proposed these crossings as possible formation triggers for various MW features, including the spiral arms, the stellar bar, the Gaia phase spiral, and disc corrugations, but have generally considered these features in isolation. We adopt a more holistic approach, testing whether a single disc-crossing impulse from a Sgr-like perturber can trigger these features simultaneously by comparing simulations to observations. We present an analysis of how the interaction shapes spiral arms, disc corrugations, the phase spiral, and the $L_{z}-\bar{V}_{R}$ wave. We find that a single disc crossing can reasonably well reproduce (e.g. structure, amplitude, phase) the observed local disc corrugation and the Outer, Local, and Sagittarius-Carina arm segments, implying that the last significant impulse due to a transit took place 700–1200Myr ago. Moreover, the $L_{z}-\bar{V}_{R}$ wave and phase spiral appear within the simulations over the same epoch and qualitatively resemble observations. We conclude that Sgr’s last significant crossing, roughly ~1 Gyr ago, could be the primary cause of many large-scale MW disc features, but it cannot fully account for all of them. Hence, other triggers, such as mergers, interactions with other satellites or with the bar, must be considered to fully explain the current dynamical state of the Galactic disc.