2011ApJ...732..124S

We present near-infrared (2.5-5.0 µm) spectra of shocked H₂gas in the supernova remnant IC 443, obtained with the satellite AKARI. Three shocked clumps–known as B, C, and G–and one background region were observed, and only H₂ emission lines were detected. Except in clump B, the extinction-corrected level population shows the ortho-to-para ratio of ∼3.0. From the level populations of clumps C and G–both the one obtained with AKARI and the one extended with previous mid-infrared observations–we found that the υ = 0 levels are more populated than the υ>0 levels at a fixed level energy, which cannot be reproduced by any combination of H₂ gas in local thermodynamic equilibrium. The populations are described by the two-density power-law thermal admixture model, revised to include the collisions with H atoms. We attributed the lower (n(H₂)=10^2.8-10^3.8/cm3) and higher (n(H₂)=10^5.4-10^5.8/cm3) density gases to the shocked H₂ gas behind C-type and J-type shocks, respectively, based on several arguments including the obtained high H I abundance n(H I)/n(H₂) = 0.01. Under the hierarchical picture of molecular clouds, the C-type and J-type shocks likely propagate into "clumps" and "clouds" (interclump media), respectively. The power-law index b of 1.6 and 3.5, mainly determined by the lower density gas, is attributed to the shock-velocity diversity, which may be a natural result during shock-cloud interactions. According to our results, H₂υ = 1 {x2192} 0 S(1) emission is mainly from J shocks propagating into interclump media. The H₂ emission was also detected at the background region, and this diffuse H₂ emission may originate from the collisional process in addition to ultraviolet photon pumping.