Three-Dimensional Kinematic Reconstruction of the Optically-Emitting,
  High-Velocity, Oxygen-Rich Ejecta of Supernova Remnant N132D
  We present a three-dimensional kinematic reconstruction of the
optically-emitting, oxygen-rich ejecta of supernova remnant N132D in the Large
Magellanic Cloud. Data were obtained with the 6.5 m Magellan telescope in
combination with the IMACS+GISMO instrument and survey [O III]
$\lambda\lambda$4959,5007 line emission in a ${\sim}$3$^{\prime}~\times$
3$^{\prime}$ region centered on N132D. The spatial and spectral resolution of
our data enable detailed examination of the optical ejecta structure. The
majority of N132D's optically bright oxygen ejecta are arranged in a torus-like
geometry tilted approximately 28$^{\circ}$ with respect to the plane of the
sky. The torus has a radius of 4.4 pc ($D_{\rm LMC}$/50 kpc), exhibits a
blue-shifted radial velocity asymmetry of $-3000$ to $+2300$ km s$^{-1}$, and
has a conspicuous break in its circumference. Assuming homologous expansion
from the geometric center of O-rich filaments, the average expansion velocity
of 1745 km s$^{-1}$ translates to an age since explosion of 2450 $\pm$ 195 yr.
A faint, spatially-separated "runaway knot" (RK) with total space velocity of
3650 km s$^{-1}$ is nearly perpendicular to the torus plane and coincident with
X-ray emission that is substantially enhanced in Si relative to the LMC and
N132D's bulk ejecta. These kinematic and chemical signatures suggest that the
RK may have had its origin deep within the progenitor star. Overall, the main
shell morphology and high-velocity, Si-enriched components of N132D have
remarkable similarity with that of Cassiopeia A, which was the result of a Type
IIb supernova explosion. Our results underscore the need for further
observations and simulations that can robustly reconcile whether the observed
morphology is dominated by explosion dynamics or shaped by interaction with the
environment.
