JWST Observations of Starbursts: Cold Clouds and Plumes Launching in the M82 Outflow

TL;DR

This study uses JWST observations to analyze the filamentary PAH emission in M82's starburst-driven wind, revealing small-scale clouds within large plumes that survive wind breakout, and correlating with other emissions.

Contribution

It provides new insights into the structure and survival of cold gas clouds in galactic outflows, supported by high-resolution JWST data and comparison with simulations.

Findings

Most PAH emission is associated with plumes extending 200-300 pc.

Small clouds within plumes are 5-15 pc wide, consistent with cloud-crushing timescales.

PAH emission correlates with Paα emission and is suppressed in X-ray bright regions.

Abstract

In this paper we study the filamentary substructure of 3.3 $\mu$m PAH emission from JWST/NIRCam observations in the base of the M82 star-burst driven wind. We identify plume-like substructure within the PAH emission with widths of $\sim$50 pc. Several of the plumes extend to the edge of the field-of-view, and thus are at least 200-300 pc in length. In this region of the outflow, the vast majority ($\sim$70\%) 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$0.5-3 Myr, depending on assumptions. We show this time scale is consistent with a picture in which these observed PAH clouds survived break-out from the disk rather than being destroyed by the hot wind. The PAH emission in both the midplane and the outflow is shown to tightly correlate with that of Pa$\alpha$ emission (from HST/NICMOS data), at the scale of both plumes and clouds, though the ratio of PAH-to-Pa$\alpha$ increases at further distances from the midplane. Finally, we show that the outflow PAH emission is suppressed in regions of the M82 wind that are bright in X-ray emission. Overall, our results are broadly consistent with a picture in which cold gas in galactic outflows is 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.