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).
@article{arxiv.astro-ph/0001336,
title = {ISO Spectroscopy of H2 in Star Forming Regions},
author = {M. E. van den Ancker and P. R. Wesselius and A. G. G. M. Tielens},
journal= {arXiv preprint arXiv:astro-ph/0001336},
year = {2007}
}
Comments
4 pages, 2 figures, to appear in proc. "H2 in Space", eds. F. Combes & G. Pineau des Forets