JWST Observations of Starbursts: Cold Clouds and Plumes Launching in the M82 Outflow
arxiv(2024)
Abstract
In this paper we study the filamentary substructure of 3.3 μm 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 ∼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 (∼70%) of PAH emission is associated with the plumes. We
show that those structures contain smaller scale "clouds" with widths that are
∼5-15 pc, and they are morphologically similar to the results of
"cloud-crushing" simulations. We estimate the cloud-crushing time-scales of
∼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
Paα emission (from HST/NICMOS data), at the scale of both plumes and
clouds, though the ratio of PAH-to-Paα 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.
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