Bending waves excited by irregular gas inflow along warps

Gaia has revealed clear evidence of bending waves in the vertical kinematics stars Solar Neighbourhood. We study two simulations, one warped, with warp due to misaligned gas inflow, and other unwarped. find slow, retrograde both models, ones warped model having larger amplitudes. also fast, prograde waves. Prograde unwarped are very weak, agreement expectation that these should decay on short, ~ crossing, timescales, strong winding. However, much stronger for duration model, pointing irregular inflow along as a continuous source excitation. demonstrate large amplitude propagate through Neighbourhood give rise correlation between mean velocity angular momentum, slope consistent found by Gaia. The affect populations all ages, but sharpest features young populations, hinting short wavelength not supported older, kinematically hotter, populations. Our results importance accretion recurrent perturbations disc galaxies, including Milky Way.