The origin and fate of the Gaia phase-space snail

Abstract

The Gaia snail is a spiral feature in the distribution of solar-neighbourhood stars in position and velocity normal to the Galactic midplane. The snail probably arises from phase mixing of gravitational disturbances that perturbed the disc in the distant past. The most common hypothesis is that the strongest disturbance resulted from a passage of the Sagittarius dwarf galaxy close to the solar neighbourhood. In this paper we investigate the alternative hypothesis that the snail is created by many small disturbances rather than one large one, that is, by Gaussian noise in the gravitational potential. Probably most of this noise is due to substructures in the dark-matter halo. We show that this hypothesis naturally reproduces most of the properties of the snail. In particular it predicts correctly, with no free parameters, that the apparent age of the snail will be $\sim 0.5$ Gyr. An important ingredient of this model is that any snail-like feature in the solar neighbourhood, whatever its cause, is erased by scattering from giant molecular clouds or other small-scale structure on a time-scale $\lesssim 1$ Gyr.

9 pages, 6 figures. Submitted to MNRAS

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• The Great Wave: Evidence of a large-scale vertical corrugation propagating outwards in the Galactic disc
• Radial phase spirals in the Solar neighbourhood
• A Comprehensive Perturbative Formalism for Phase Mixing in Perturbed Disks. II. Phase Spirals in an Inhomogeneous Disk Galaxy with a Non-responsive Dark Matter Halo
• Ripples spreading across the Galactic disc. Interplay of direct and indirect effects of the Sagittarius dwarf impact
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• Galactic disc heating by density granulation in fuzzy dark matter simulations
• A non-axisymmetric potential for the Milky Way disk
• Limitations and rotation of the two-armed phase spiral in the Milky Way stellar disc
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• Galactic echoes
• Fundamental limits to orbit reconstruction due to non-conservation of stellar actions in a Milky Way-like simulation
• Delayed phase mixing in the self-gravitating Galactic disc
• An analytic description of substructure-induced gravitational perturbations in stellar systems
• Evolution of action-space coherence in a Milky Way-like simulation
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• Wrinkles in Time. II. Stellar Age Trends in Kinematic Signatures from Transient Spiral Structure
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