Phase spirals induced by the gas warp

TL;DR

This study demonstrates that irregular gas inflow along the galactic warp can induce long-lived phase spirals in the Milky Way, providing a new perspective on their origin and evolution.

Contribution

The paper introduces warp-induced gas inflow as a novel mechanism for generating persistent phase spirals in galaxy discs.

Findings

Strong, long-lived phase spirals are produced in warped galaxy simulations.

Phase spiral morphology varies with location and time, correlating with gas inflow and bending wave amplitude.

Unwarped simulations show weak, stochastic phase spirals, highlighting the role of warps.

Abstract

The discovery of the phase space spirals in the Solar neighborhood in Gaia Data Release 2 has prompted various attempts to understand their origin. A source of bending waves, which has been neglected as a cause of the phase spiral, is irregular gas inflow along the warp. We aim to study whether perturbations by the gas warp could induce phase spirals. Accounting for this additional formation scenario for phase spirals could improve our current understanding of the perturbation history of the Milky Way disc. We use two N-body + SPH (Smooth Particle Hydrodynamics) simulations of an isolated galaxy to search for, and study, warp-induced phase spirals. We study the emergence and propagation of the detected phase spirals using Fourier decomposition. We detect strong one-armed phase spirals in the warped simulation. These phase spirals are prevalent and persist over ~10 Gyr. The morphology of these phase spirals varies with location and evolves with time. In particular, the emergence rate of the phase spiral evolves with the gas inflow at the outer disc and the bending wave amplitude, indicating that these phase spirals are a record of warp-induced bending waves. We find that these phase spirals can reach amplitudes comparable to those in the Gaia DR3. We only detect weak and stochastically distributed phase spirals in an unwarped control simulation. We conclude that phase spirals can be induced by the irregular gas accretion along the warp. These phase spirals occur globally and are long-lived.