Bon-Chul

Supernova remnants (SNRs) are one of prominent objects in infrared (IR) emission, and their Infrared-to-X-ray (IRX) flux ratios are generally thought to indicate the relative importance of dust cooling to gas cooling in hot dusty plasma. But recent high-resolution IR space missions show that SNRs have diverse morphology in IR dust emission often very different from their X-ray appearance, suggesting different origins for the IR dust emission. We explored how the natural and/or environmental properties of SNRs affect the IRX morphology of SNRs and their IRX flux ratios.

We first investigated IR and X-ray properties of 20 Galactic SNRs that are relatively well defined in both bands. We found that the observed IRX flux ratios of some SNRs agree with theoretical ratios of SNR shocks in which dust grains are heated and destroyed by collisions with plasma particles. For the majority of SNRs, however, the IRX flux ratios are either significantly smaller or significantly larger than the theoretical ratios. The SNRs with the smallest IRX flux ratios are young SNRs with X-ray emission dominated by metal-rich SN ejecta. There are, however, also evolved SNRs with good IRX morphological correlation but have small IRX flux ratios. For these SNRs, low dust-to-gas ratio (DGR) of the ambient medium seems to be a plausible explanation. On the other hand, the SNRs with the largest IRX flux ratios
have anticorrelated IRX morphology and relatively low dust temperatures.
We have found that these SNRs are located in dense environment, and their IR emission is probably from dust heated by shock radiation rather than by collisions.

We also derived IRX flux ratios of SNRs in the Large Magellanic Cloud (LMC) using {it Spitzer} and {it Chandra} SNR survey data and compared them with those of Galactic SNRs. We found that the IRX flux ratios of the LMC SNRs are systematically lower than those of the Galactic SNRs, which appears to be consistent with the low DGR of the LMC. We also confirmed the relation between IRX flux ratios and the IRX morphology. We will discuss the implications of our results for the study of SNRs in external galaxies.