Widespread corrugations superimposed on the Galactic warp in the outer CO disk

Vertical corrugations—wave-like undulations in galactic disks—are potential imprints of past dynamical events that offer key constraints on galaxy evolution. While large-scale corrugations superimposed on the Galactic warp have recently been detected using young stellar tracers, the corresponding widespread structure within the molecular gas remains largely unexplored due to the challenge of disentangling subtle amplitudes from the dominant warp signal. By analysing over 30,000 molecular clouds from the Milky Way Imaging Scroll Painting survey, we systematically characterize widespread corrugations across the outer CO disk. After subtracting a global CO warp model, residual vertical displacements reveal coherent wave-like structures spanning much of the outer disk. Quantitative modelling yields characteristic vertical amplitudes of ~100–200 pc and radial wavelengths of ~3.9–7.9 kpc, and identifies a coherent azimuthal corrugation mode with a 52.6° (~11.6 kpc) wavelength at Galactocentric radius R ≈ 12.7 kpc, extending ~40 kpc. These findings provide direct evidence that vertical corrugations are a common large-scale feature of the outer Galactic molecular disk, offering insights into the three-dimensional structure and dynamics of spiral galaxies. Using more than 30,000 molecular clouds, this study reveals widespread wave-like corrugations superimposed on the warp of the Milky Way’s outer molecular disk, offering insight into its three-dimensional structure and dynamics.