Ultraviolet Excited High-J Molecular Hydrogen in Photodissociation Regions

Details Ultraviolet Excited High-J Molecular Hydrogen in Photodissociation Regions Ultraviolet Excited High-J Molecular Hydrogen in Photodissociation Regions

Feb 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007apj...655..940l&link_type=abstract

The Astrophysical Journal, Volume 655, Issue 2, pp. 940-945.

Astronomy and Astrophysics

Astronomy

6

Ism: Clouds, Line: Profiles, Ultraviolet: Ism

Scientific paper

We have calculated synthetic interstellar cloud models to investigate the formation and destruction of high-J molecular hydrogen in photodissociation regions. The effects of five physical parameters (the incident ultraviolet [UV] intensity, H2 column density, cloud temperature, total density, and H2 formation rate coefficient) on the populations of H2 rotational levels are explored. We have found that N(4)/N(0) is proportional to the incident UV intensity IUV and the H2 molecular fraction f is simply related to the ratio of IUV and the hydrogen density nH, implying a new method to derive IUV and nH with the observational parameters N(4)/N(0) and f, assuming an H2 formation rate R. High-resolution FUSE spectra of H2 toward three translucent sight lines (HD 110432, HD 192639, and HD 185418) in the Milky Way and 24 diffuse sight lines in the SMC and LMC are referenced to obtain N(4)/N(0) and f. Using our method, we are able to derive IUV~10-40 for the translucent sight lines, when R is assumed to be 10 times higher than the Galactic value. Synthetic models for the Magellanic sight lines suggest that IUV>=10, nH<=100 cm-3, and R~3×10-16 for the low H2 column density sight lines (N[H2]<=1018 cm-2) and IUV>=10, nH<=1000 cm-3, and R~3×10-17 for the high H2 column density sight lines (N[H2]>=1019 cm-2).

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