Grand, Robert J. J., Pakmor, Ruediger, Fragkoudi, Francesca, Gomez, Facundo A., Trick, Wilma, Simpson, Christine M., van de Voort, Freeke, Bieri, Rebekka2024-11-272024-11-272023/07/040035-8711http://dx.doi.org/10.1093/mnras/stad1969https://publicacionesabiertas.userena.cl/handle/123456789/102We utilize a novel numerical technique to model star formation in cosmological simulations of galaxy formation - called SUPERSTARS - to simulate a Milky Way-like galaxy with greater than or similar to 10(8) star particles to study the formation and evolution of out-of-equilibrium stellar disc structures in a full cosmological setting. In the plane defined by the coordinate and velocity perpendicular to the mid-plane [vertical phase space, (Z, V-Z)], stars in solar- like volumes at late times exhibit clear spirals qualitatively similar in shape and amplitude to the Gaia 'snail shell' phase spiral. We show that the phase spiral forms at a lookback time of similar to 6 Gyr during the pericentric passage of an similar to 10(10) M-circle dot satellite on a polar orbit. This satellite stimulates the formation of a resonant wake in the dark matter halo while losing mass at a rate of similar to 0.5-1 dex per orbit loop. The peak magnitude of the wake-induced gravitational torque at the solar radius is similar to 8 times that from the satellite, and triggers the formation of a disc warp that wraps up into a vertical phase spiral over time. As the wake decays, the phase spiral propagates several gigayears to present day and can be described as `ever-present' once stable disc evolution is established. These results suggest an alternative scenario to explain the Gaia phase spiral, which does not rely on a perturbation from bar buckling or a recent direct hit from a satellite.PHASE-SPACE SPIRALS, MILKY-WAY DISC, COSMOLOGICAL SIMULATIONS, STELLAR MOTIONS, GALACTIC DISK, GALAXY, SAGITTARIUS, WAVES, HALO, MODELArticle