Snails Across Scales: Local and Global Phase-Mixing Structures as Probes of the Past and Future Milky Way

Abstract

Signatures of vertical disequilibrium have been observed across the Milky Way's disk. These signatures manifest locally as unmixed phase-spirals in $z$--$v_z$ space ("snails-in-phase") and globally as nonzero mean $z$ and $v_z$ which wraps around as a physical spiral across the $x$--$y$ plane ("snails-in-space"). We explore the connection between these local and global spirals through the example of a satellite perturbing a test-particle Milky Way (MW)-like disk. We anticipate our results to broadly apply to any vertical perturbation. Using a $z$--$v_z$ asymmetry metric we demonstrate that in test-particle simulations: (a) multiple local phase-spiral morphologies appear when stars are binned by azimuthal action $J_{\varphi }$, excited by a single event (in our case, a satellite disk-crossing); (b) these distinct phase-spirals are traced back to distinct disk locations; and (c) they are excited at distinct times. Thus, local phase-spirals offer a global view of the MW's perturbation history from multiple perspectives. Using a toy model for a Sagittarius (Sgr)-like satellite crossing the disk, we show that the full interaction takes place on timescales comparable to orbital periods of disk stars within $R\lesssim 10$ kpc. Hence such perturbations have widespread influence which peaks in distinct regions of the disk at different times. This leads us to examine the ongoing MW-Sgr interaction. While Sgr has not yet crossed the disk (currently, $z_{Sgr}\approx -6$ kpc, $v_{z,Sgr}\approx 210$ km/s), we demonstrate that the peak of the impact has already passed. Sgr's pull over the past 150 Myr creates a global $v_z$ signature with amplitude $\propto M_{Sgr}$, which might be detectable in future spectroscopic surveys.

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Cited by in corpus (14)

• Galactic Archaeology with Gaia
• Multiple phase spirals suggest multiple origins in Gaia DR3
• The phase spiral in Gaia DR3
• Vertical motion in the Galactic disc: unwinding the Snail
• A Comprehensive Perturbative Formalism for Phase-Mixing in Perturbed Disks. I. Phase spirals in an Infinite, Isothermal Slab
• 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
• Investigating the amplitude and rotation of the phase spiral in the Milky Way outer disc
• Ripples spreading across the Galactic disc. Interplay of direct and indirect effects of the Sagittarius dwarf impact
• Radial Wave in the Galactic Disk: New Clues to Discriminate Different Perturbations
• A barred Milky Way surrogate from an N-body simulation
• Two-point correlation function studies for the Milky Way: discovery of spatial clustering from disk excitations and substructure
• Delayed phase mixing in the self-gravitating Galactic disc
• The disturbed outer Milky Way disc