科研之友
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摘要
We present near-infrared (2.5-5.0 mu m) spectra of shocked H-2 gas 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 H-2 emission lines were detected. Except in clump B, the extinction-corrected level population shows the ortho-to-para ratio of similar to 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 nu = 0 levels are more populated than the nu > 0 levels at a fixed level energy, which cannot be reproduced by any combination of H-2 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(H-2)= 10(2.8)-10(3.8) cm(-3)) and higher (n(H-2)= 10(5.4)-10(5.8) cm(-3)) density gases to the shocked H-2 gas behind C-type and J-type shocks, respectively, based on several arguments including the obtained high HI abundance n(H I)/n(H-2) = 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, H-2 nu = 1 -> 0 S(1) emission is mainly from J shocks propagating into interclump media. The H-2 emission was also detected at the background region, and this diffuse H-2 emission may originate from the collisional process in addition to ultraviolet photon pumping.
- 出版日期2011-5-10
