2020ApJ...899...49K

We investigate properties of the interstellar medium (ISM) interacting with shocks around the Galactic supernova remnant IC 443, using the results of near-infrared [Fe II] and H₂ line mapping with the InfraRed Survey Facility/Simultaneous Infrared Imager for Unbiased Survey. In the present study, we newly performed H₂ 1-0 S(1) and 2-1 S(1) line mapping with the narrowband filters tuned for these lines, covering the entire remnant (30^′ × 35^′ ). Combined with an [Fe II] line map, our result shows that the H₂ line emission is significantly detected in the southern region, while the [Fe II] line emission is detected all over the remnant, suggesting that slow and fast shocks propagate through the southern region and the entire remnant, respectively. In particular, the H₂ line emission is relatively strong compared to the [Fe II] line emission in the southwestern region, where TeV γ-ray emission is detected. As the strong H₂ line emission indicates the dominance of the dense ISM, this result supports the scenario that the γ-ray emission is likely to be produced through a heavy interaction between cosmic-ray protons and the dense ISM in the southwestern shell. We also find that the H₂ and [Fe II] line emissions show an anti-correlated spatial distribution in the same region, suggesting the presence of the clumpy ISM. Such a clumpy morphology of the ISM around IC 443 may assist cosmic-ray protons to efficiently interact with large amounts of the ISM protons.