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ISO Spectroscopy of H2 in Star Forming Regions

M. E. van den Ancker·P. R. Wesselius·A. G. G. M. Tielens
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Abstract

We have studied molecular hydrogen emission in a sample of 21 YSOs using spectra obtained with the Infrared Space Observatory (ISO). H2 emission was detected in 12 sources and can be explained as arising in either a shock, caused by the interaction of an outflow from an embedded YSO with the surrounding molecular cloud, or in a PDR surrounding an exposed young early-type star. The distinction between these two mechanisms can not always be made from the pure rotational H2 lines alone. Other tracers, such as PAH emission or [S I] 25.25 micron emission, are needed to identify the H2 heating mechanism. No deviations from a 3:1 ortho/para ratio of H2 were found. Both shocks and PDRs show a warm and a hot component in H2, which we explain as thermal emission from warm molecular gas (warm component), or UV-pumped infrared fluorescence in the case of PDRs and the re-formation of H2 for shocks (hot component).

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M. E. van den Ancker, P. R. Wesselius, A. G. G. M. Tielens. 2000-01-19. ISO Spectroscopy of H2 in Star Forming Regions. https://arxiv.org/abs/astro-ph/0001336

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