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

Grand, RJJ, Pakmor, R, Fragkoudi, F, Gómez, FA, Trick, W, Simpson, CM, van de Voort, F and Bieri, R (2023) An ever-present Gaia snail shell triggered by a dark matter wake. Monthly Notices of the Royal Astronomical Society, 524 (1). pp. 801-816. ISSN 0035-8711

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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 ≳108 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, VZ)], 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 ∼6 Gyr during the pericentric passage of an ∼1010 M. 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 ∼0.5–1 dex per orbit loop. The peak magnitude of the wake-induced gravitational torque at the solar radius is ∼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.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
SWORD Depositor: A Symplectic
Date Deposited: 24 Jul 2023 10:45
Last Modified: 24 Jul 2023 10:45
DOI or ID number: 10.1093/mnras/stad1969
URI: https://researchonline.ljmu.ac.uk/id/eprint/20495
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