Phase-space spirals as probes of perturbed, out-of-equilibrium disk galaxies

Disk galaxies are highly responsive systems that undergo oscillations triggered by various agents such as external forces and tides from satellite galaxies and dark matter substructure. Such gravitational interactions tend to throw disk galaxies out of equilibrium. In due course, stellar oscillations lose coherence and perturbations damp out by collisionless relaxation mechanisms like phase-mixing and Landau damping, which manifest as phase-space spirals. These dynamical features have recently been observed by GAIA in our Milky Way galaxy, hinting at the possibility of recent interactions in the galactic disk. In this talk I shall demonstrate a general perturbative formalism to compute the disk response to various perturbers such as spiral arms and satellite galaxies and obtain the resultant phase-space spirals. Using this formalism, I shall elucidate the perturber characteristics responsible for triggering bending and breathing oscillation modes corresponding to one- and two-armed phase-space spirals. This can be used to constrain the Milky Way’s dynamical history. I shall also discuss the survivability and observability of phase-space spirals in the galactic disk, and illustrate their usefulness as probes of the galactic potential.