paper

An ever-present snail shell triggered by a dark matter wake

arXiv:2211.08437 · doi:10.1093/mnras/stad1969

Abstract

We 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 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, ), stars in Solar-like volumes at late times exhibit clear spirals qualitatively similar in shape and amplitude to the ``Snail shell'' phase spiral. We show that the phase spiral forms at a look back time of Gyr during the pericentric passage of a 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 - dex per orbit loop. The peak magnitude of the wake-induced gravitational torque at the Solar radius is 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 phase spiral which does not rely on a perturbation from bar buckling or a recent direct hit from a satellite.

arXiv commentaccepted for pub in mnras. 11 + 5 pages. For a high-cadence animated version of figure 1, see https://wwwmpa.mpa-garching.mpg.de/auriga/movies/multi_halo_6_sf64.mp4

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