Astronomers have identified widespread vertical wave-like corrugations across the outer molecular gas disk of the Milky Way, Nature Astronomy reported. Researchers at the Purple Mountain Observatory of the Chinese Academy of Sciences mapped the undulations by analyzing more than 30,000 molecular clouds.
The study, led by Yan Sun, Shaobo Zhang, and Ji Yang, used data from the Milky Way Imaging Scroll Painting survey along the northern Galactic plane. The survey observed multiline carbon monoxide emissions in 12CO, 13CO, and C18O using the PMO 13.7-meter millimeter-wave radio telescope.
Large-scale corrugations superimposed on the Galactic warp had previously been traced using young stars, such as classical Cepheids and young giant stars. Detecting corresponding patterns in molecular gas had proved difficult because the dominant Galactic warp signal masked subtle vertical shifts.
To isolate the corrugations, the researchers fitted and subtracted global carbon monoxide warp models from the cloud distribution. Residual vertical displacements showed coherent wave structures across the outer disk. Quantitative modeling yielded characteristic vertical amplitudes of approximately 100 to 200 parsecs and radial wavelengths of roughly 3.9 to 7.9 kiloparsecs. At a Galactocentric radius of about 12.7 kiloparsecs, the analysis identified a coherent azimuthal corrugation mode with a wavelength of 52.6 degrees (around 11.6 kiloparsecs) extending across approximately 40 kiloparsecs.
Empirical forward-modeling tests demonstrated that kinematic distance errors and streaming perturbations did not produce the observed features. The team made the molecular cloud catalog accessible on Science Data Bank, and the Python modeling code was deposited on GitHub and Zenodo.
