Infrared Supernova Remnants and their Infrared to X-ray Flux Ratios

TL;DR

This study investigates the diverse infrared to X-ray flux ratios in supernova remnants, revealing their dependence on morphology and environment, and proposes using IRX ratios and dust temperature to infer properties of unresolved SNRs.

Contribution

It provides a detailed analysis of IRX flux ratios in 20 Galactic SNRs, linking these ratios to morphology, environment, and shock heating processes, and suggests their use in studying unresolved SNRs in other galaxies.

Findings

IRX flux ratios vary widely among SNRs.

Largest IRX ratios are associated with dense environments.

IR emission in some SNRs is dominated by shock-heated dust.

Abstract

Recent high-resolution infrared space missions have revealed supernova remnants (SNRs) of diverse morphology in infrared (IR) dust emission that is often very different from their X-ray appearance. The observed range of infrared-to-X-ray (IRX) flux ratios of SNRs are also wide. For a sample of 20 Galactic SNRs, we obtain their IR and X-ray properties and investigate the physical causes for such large differences. We find that the observed IRX flux ratios ($R_{IRX.obs}$) are related to the IRX morphology, with SNRs with the largest $R_{IRX,obs}$ showing anticorrelated IRX morphology. By analyzing the relation of $R_{IRX,obs}$ to X-ray and IR parameters, we show that the $R_{IRX,obs}$ 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, $R_{IRX,obs}$ values are either significantly smaller or significantly larger than the theoretical ratios. The latter SNRs have relatively low dust temperatures. We discuss how the natural and/or environmental properties of SNRs could have affected the IRX flux ratios and the IRX morphology of these SNRs. We conclude that the SNRs with largest $R_{IRX,obs}$ are probably located in dense environment and that their IR emission is from dust heated by shock radiation rather than by collisions. Our result suggests that the IRX flux ratio, together with dust temperature, can be used to infer the nature of unresolved SNRs in external galaxies.