The origin and fate of the Gaia phase-space snail

TL;DR

The paper proposes that the Gaia snail feature results from Gaussian noise in the gravitational potential, likely due to dark matter substructures, rather than a single large disturbance like the Sagittarius dwarf galaxy.

Contribution

It introduces a novel hypothesis that the Gaia snail is caused by multiple small disturbances, successfully reproducing its properties without free parameters.

Findings

The noise hypothesis predicts the snail's age as approximately 0.5 Gyr.

The snail feature is erased within about 1 Gyr by scattering from molecular clouds.

The model aligns with observed properties of the Gaia 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.