Dust Cooling in Supernova Remnants in the Large Magellanic Cloud

TL;DR

This study examines dust and gas cooling in supernova remnants within the Large Magellanic Cloud, revealing dust's significant role and differences from Galactic remnants, influenced by the local interstellar medium properties.

Contribution

It provides the first systematic comparison of IRX ratios in LMC and Galactic SNRs, highlighting the impact of dust-to-gas ratio variations on cooling processes.

Findings

IRX ratios are moderately greater than unity, indicating dust cooling dominance.

LMC SNRs have systematically lower IRX ratios than Galactic SNRs.

Discrepancies with theoretical models suggest dust depletion or destruction affects IRX ratios.

Abstract

The infrared-to-X-ray (IRX) flux ratio traces the relative importance of dust cooling to gas cooling in astrophysical plasma such as supernova remnants (SNRs). We derive IRX ratios of SNRs in the LMC using Spitzer and Chandra SNR survey data and compare them with those of Galactic SNRs. IRX ratios of all the SNRs in the sample are found to be moderately greater than unity, indicating that dust grains are a more efficient coolant than gas although gas cooling may not be negligible. The IRX ratios of the LMC SNRs are systematically lower than those of the Galactic SNRs. As both dust cooling and gas cooling pertain to the properties of the interstellar medium, the lower IRX ratios of the LMC SNRs may reflect the characteristics of the LMC, and the lower dust-to- gas ratio (a quarter of the Galactic value) is likely to be the most significant factor. The observed IRX ratios are compared with theoretical predictions that yield IRX ratios an order of magnitude larger. This discrepancy may originate from the dearth of dust in the remnants due to either the local variation of the dust abundance in the preshock medium with respect to the canonical abundance or the dust destruction in the postshock medium. The non-equilibrium ionization cooling of hot gas, in particular for young SNRs, may also cause the discrepancy. Finally, we discuss implications for the dominant cooling mechanism of SNRs in low-metallicity galaxies.