Infrared [Fe II] and Dust Emissions from Supernova Remnants

TL;DR

This paper reviews infrared emissions from supernova remnants, focusing on [Fe II] lines and dust, highlighting their diagnostic value for different SNR environments and evolutionary stages.

Contribution

It provides a comprehensive overview of infrared emission mechanisms in SNRs, including [Fe II] and dust, and discusses their implications for understanding SNR evolution and supernova rates.

Findings

Two groups of [Fe II]-bright SNRs identified: interacting with molecular clouds and young core-collapse remnants.

Correlation between [Fe II] and H₂ emissions indicating atomic and molecular shocks coexist.

Detection of SN dust and crystalline silicates in SNRs.

Abstract

Supernova remnants (SNRs) are strong thermal emitters of infrared radiation. The most prominent lines in the near-infrared spectra of SNRs are [Fe II] lines. The [Fe II] lines are from shocked dense atomic gases, so they trace SNRs in dense environments. After briefly reviewing the physics of the [Fe II] emission in SNR shocks, I describe the observational results which show that there are two groups of SNRs bright in [Fe II] emission: middle-aged SNRs interacting with molecular clouds and young core-collapse SNRs in dense circumstellar medium. The SNRs belonging to the former group are also bright in near-infrared H$_2$ emission, indicating that both atomic and molecular shocks are pervasive in these SNRs. The SNRs belonging to the latter group have relatively small radii in general, implying that most of them are likely the remnants of SN IIL/b or SN IIn that had strong mass loss before the explosion. I also comment on the "[Fe II]-H$_2$ reversal" in SNRs and on using the [Fe II]-line luminosity as an indicator of the supernova (SN) rate in galaxies. In the mid- and far-infrared regimes, thermal dust emission is dominant. The dust in SNRs can be heated either by collisions with gas species in a hot plasma or by radiation from a shock front. I discuss the characteristics of the infrared morphology of the SNRs interacting with molecular clouds and their dust heating processes. Finally, I give a brief summary of the detection of SN dust and crystalline silicate dust in SNRs.