Breaking Orion's Veil bubble with fossil outflows
  The role of feedback in the self-regulation of star formation is a
fundamental question in astrophysics. The Orion Nebula is the nearest site of
ongoing and recent massive star formation. It is a unique laboratory for the
study of stellar feedback. Recent SOFIA [CII] 158 $\mu$m observations revealed
an expanding bubble, the Veil shell, being powered by stellar winds and
ionization feedback. We have identified a protrusion-like substructure in the
Northwest portion of the Orion Veil Shell that may indicate additional feedback
mechanisms that are highly directional. Our goal is to investigate the origin
of the protrusion by quantifying its possible driving mechanisms. We use the
[CII] 158 $\mu$m map of the Orion Nebula obtained with the upGREAT instrument
onboard SOFIA. The spectral and spatial resolution of the observations are 0.3
km/s and 16 arcsec, respectively.
  We consider three possible origins for this protrusion: Fossil outflow
cavities created by jets/outflows during the protostellar accretion phase,
pre-existing clumpiness in the OMC-1 core, and the stellar wind during the main
sequence phase. Based on the energetics and the morphology, we conclude that
the northwestern part of the pre-existing cloud was locally perturbed by
outflows ejected from massive protostars in the Trapezium cluster. This
suggests that the protrusion of the Veil is the result of mechanical rather
than radiative feedback. Furthermore, we argue that the location of the
protrusion is a suitable place to break the Orion Veil owing to the
photo-ablation from the walls of the protrusion. We conclude that the outflows
of massive protostars can influence the morphology of the future \hii\,region
and even cause breakages in the ionization front. Specifically, the interaction
of stellar winds of main-sequence stars with the molecular core pre-processed
by the protostellar jet is important.
