ALMA CO Observations of Gamma-Ray Supernova Remnant N132D in the Large
  Magellanic Cloud: Possible Evidence for Shocked Molecular Clouds Illuminated
  by Cosmic-Ray Protons
  N132D is the brightest gamma-ray supernova remnant (SNR) in the Large
Magellanic Cloud (LMC). We carried out $^{12}$CO($J$ = 1-0, 3-2) observations
toward the SNR using the Atacama Large Millimeter/submillimeter Array (ALMA)
and Atacama Submillimeter Telescope Experiment. We find diffuse CO emission not
only at the southern edge of the SNR as previously known, but also inside the
X-ray shell. We spatially resolved nine molecular clouds using ALMA with an
angular resolution of $5''$, corresponding to a spatial resolution of $\sim$1
pc at the distance of the LMC. Typical cloud sizes and masses are $\sim$2.0 pc
and $\sim$100 $M_\odot$, respectively. High-intensity ratios of CO $J$ = 3-2 /
1-0 $> 1.5$ are seen toward the molecular clouds, indicating that shock-heating
has occurred. Spatially resolved X-ray spectroscopy reveals that thermal X-rays
in the center of N132D are produced not only behind a molecular cloud, but also
in front of it. Considering the absence of a thermal component associated with
the forward shock towards one molecular cloud located along the line of sight
to the center of the remnant, this suggests that this particular cloud is
engulfed by shock waves and is positioned on the near side of remnant. If the
hadronic process is the dominant contributor to the gamma-ray emission, the
shock-engulfed clouds play a role as targets for cosmic-rays. We estimate the
total energy of cosmic-ray protons accelerated in N132D to be $\sim$0.5-$3.8
\times 10^{49}$ erg as a conservative lower limit, which is similar to that
observed in Galactic gamma-ray SNRs.
