2025MNRAS.538.3068F

In this paper, we study the filamentary substructure of 3.3 $\mu$m polycyclic aromatic hydrocarbon (PAH) emission from JWST/NIRCam observations in the base of the M 82 star-burst driven wind. We identify plume-like substructure within the PAH emission with widths of $\sim$50 pc. Several of those plumes extend to the edge of the field-of-view, and thus are at least 200-300 pc in length. In this region of the outflow, the vast majority ($\sim$70 per cent) of PAH emission is associated with the plumes. We show that those structures contain smaller scale 'clouds' with widths that are $\sim$5-15 pc, and they are morphologically similar to the results of 'cloud-crushing' simulations. We estimate the cloud-crushing time-scales of $\sim$0.5-3 Myr, depending on assumptions. We show this time-scale is consistent with a picture in which these observed PAH clouds survived break-out from the disc rather than being destroyed by the hot wind. The PAH emission in both the mid-plane and the outflow is shown to tightly correlate with that of Pa $\alpha$ emission (from Hubble Space Telescope data), at the scale of both plumes and clouds, though the ratio of PAH-to-Pa $\alpha$ increases at further distances from the mid-plane. Finally, we show that the outflow PAH emission reaches a local minimum in regions of the M 82 wind that are bright in X-ray emission. Our results are consistent cold gas in galactic outflows being launched via hierarchically structured plumes, and those small scale clouds are more likely to survive the wind environment when collected into the larger plume structure.