A survey of infrared supernova remnants in the Large Magellanic Cloud
  We present a comprehensive infrared study of supernova remnants (SNRs) in the
Large Magellanic Cloud (LMC) using near- to mid-infrared images taken by
Infrared Array Camera (IRAC; 3.6, 4.5, 5.8, and 8 {\mu}m) and Multiband Imaging
Photometer (MIPS; 24 and 70 {\mu}m) onboard the Spitzer Space Telescope. Among
the 47 bona fide LMC SNRs, 29 were detected in infrared, giving a high
detection rate of 62%. All 29 SNRs show emission at 24 {\mu}m, and 20 out of 29
show emission in one or several IRAC bands. We present their 4.5, 8, 24, and 70
{\mu}m images and a table summarizing their Spitzer fluxes. We find that the
LMC SNRs are considerably fainter than the Galactic SNRs, and that, among the
LMC SNRs, Type Ia SNRs are significantly fainter than core-collapse SNRs. We
conclude that the MIPS emission of essentially all SNRs origi- nates from dust
emission, whereas their IRAC emissions originate from ionic/molecular lines,
polycyclic aromatic hydrocarbons emission, or synchrotron emission. The
infrared fluxes show correlation with radio and X-ray fluxes. For SNRs that
have similar mor- phology in infrared and X-rays, the ratios of 24 to 70 {\mu}m
fluxes have good correlation with the electron density of hot plasma. The
overall correlation is explained well by the emission from collisionally-heated
silicate grains of 0.1 {\mu}m size, but for mature SNRs with relatively low gas
temperatures, the smaller-sized grain population is favored more. For those
that appear different between infrared and X-rays, the emission in the MIPS
bands is probably from dust heated by shock radiation.
