A Comprehensive Perturbative Formalism for Phase-Mixing in Perturbed Disks. I. Phase spirals in an Infinite, Isothermal Slab

Abstract

Galactic disks are highly responsive systems that often undergo external perturbations and subsequent collisionless equilibration, predominantly via phase-mixing. We use linear perturbation theory to study the response of infinite isothermal slab analogues of disks to perturbations with diverse spatio-temporal characteristics. Without self-gravity of the response, the dominant Fourier modes that get excited in a disk are the bending and breathing modes, which, due to vertical phase-mixing, trigger local phase-space spirals that are one- and two-armed, respectively. We demonstrate how the lateral streaming motion of slab stars causes phase spirals to damp out over time. The ratio of the perturbation timescale (${\tau }_{\mathrm{P}}$) to the local, vertical oscillation time (${\tau }_z$) ultimately decides which of the two modes is excited. Faster, more impulsive (${\tau }_{\mathrm{P}}<{\tau }_z$) and slower, more adiabatic (${\tau }_{\mathrm{P}}>{\tau }_z$) perturbations excite stronger breathing and bending modes, respectively, although the response to very slow perturbations is exponentially suppressed. For encounters with satellite galaxies, this translates to more distant and more perpendicular encounters triggering stronger bending modes. We compute the direct response of the Milky Way disk to several of its satellite galaxies, and find that recent encounters with all of them excite bending modes in the Solar neighborhood. The encounter with Sagittarius triggers a response that is at least $1-2$ orders of magnitude larger than that due to any other satellite, including the Large Magellanic Cloud. We briefly discuss how ignoring the presence of a dark matter halo and the self-gravity of the response might impact our conclusions.

Accepted for publication in ApJ; 7 figures, 1 table

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Cited by in corpus (19)

• The rapid onset of stellar bars in the baryon-dominated centers of disk galaxies
• The phase spiral in Gaia DR3
• The origin and fate of the Gaia phase-space snail
• Vertical motion in the Galactic disc: unwinding the Snail
• Swing Amplification and the Gaia Phase Spirals
• Gaia DR3 features of the phase spiral and its possible relation to internal perturbations
• 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
• Growing Local arm inferred by the breathing motion
• Galactic disc heating by density granulation in fuzzy dark matter simulations
• Limitations and rotation of the two-armed phase spiral in the Milky Way stellar disc
• Two-point correlation function studies for the Milky Way: discovery of spatial clustering from disk excitations and substructure
• Galactic echoes
• Impulsive mixing of stellar populations in dwarf spheroidal galaxies
• Delayed phase mixing in the self-gravitating Galactic disc
• Minimum-entropy constraints on galactic potentials
• Chaos in violent relaxation dynamics. Disentangling micro- and macro-chaos in numerical experiments of dissipationless collapse
• The multiple corrugations in the Galactic disk derived from the LAMOST and Gaia survey data
• Correlation between the two-armed $V_R$ spiral in the $Z$--$V_Z$ plane and moving groups