Phase spirals induced by the gas warp

The discovery of the phase space-spirals in the Solar neighborhood in Data Release 2 has prompted various attempts to understand their origin. A source of bending waves that has been neglected as a cause of the phase spiral is irregular gas inflow along the warp. We studied 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 disk. We used two N-body--smoothed particle hydrodynamics (SPH) simulations of an isolated galaxy to search for and study warp-induced phase spirals. We studied 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 sim10 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 disk 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 DR3. We only detect weak and stochastically distributed phase spirals in an unwarped control simulation. We conclude that phase spirals can be induced by irregular gas accretion along the warp. These phase spirals occur globally and are long-lived.