Discovery of a coherent, wave-like velocity pattern for the Radcliffe wave

Abstract

Recent studies discovered that part of the Gould Belt belongs to a 2.7 kpc-long coherent, thin wave consisting of a chain of clouds, where a damped undulation pattern has been identified from the spatial arrangement of the clouds. We use the proper motions of young stellar objects anchored inside the clouds to study the kinematic structure of the Radcliffe wave in terms of v_z, and identify a damped, wave-like pattern from the v_z space, which we call 'velocity undulation'. We propose a new formalism based on the ensemble empirical mode decomposition to determine the amplitude, period, and phase of the undulation pattern, and find that the spatial and velocity undulation share an almost identical spatial frequency of about 1.5 kpc, and both are damped when measured from one side to the other. Measured for the first cycle, they exhibit a phase difference of around 2π/3. The structure is oscillating around the mid-plane of the Milky Way disc with an amplitude of ${\sim}130\, \pm \, 20\, \rm pc$. The vertical extent of the Radcliffe wave exceeds the thickness of the molecular disc, suggesting that the undulation of the undulation signature might originate from a perturbation, e.g. the passage of a dwarf galaxy.