Abstract
We present the results of a mid-infrared survey of 11 outer Galaxy
massive star-forming regions and 3 open clusters with data from
the Wide-field Infrared Survey Explorer (WISE). Using a newly
developed photometric scheme to identify young stellar objects
and exclude extragalactic contamination, we have studied the
distribution of young stars within each region. These data tend
to support the hypothesis that latter generations may be
triggered by the interaction of winds and radiation from the
first burst of massive star formation with the molecular cloud
material leftover from that earlier generation of stars. We dub
this process the ''fireworks hypothesis'' since star formation
by this mechanism would proceed rapidly and resemble a burst of
fireworks. We have also analyzed small cutout WISE images of the
structures around the edges of these massive star-forming
regions. We observe large (1-3 pc size) pillar and trunk-like
structures of diffuse emission nebulosity tracing excited
polycyclic aromatic hydrocarbon molecules and small dust grains
at the perimeter of the massive star-forming regions. These
structures contain small clusters of emerging Class I and Class
II sources, but some are forming only a single to a few new
stars.
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