Molecular hydrogen formation on dust grains in the high redshift universe

S. Cazaux; M. Spaans

doi:10.1086/422087

paper

Molecular hydrogen formation on dust grains in the high redshift universe

arXiv:astro-ph/0404340 · doi:10.1086/422087

Abstract

We study the formation of molecular hydrogen on dust grain surfaces and apply our results to the high redshift universe. We find that a range of physical parameters, in particular dust temperature and gas temperature, but not so much dust surface composition, influence the formation rate of H $_{2}$ . The H $_{2}$ formation rate is found to be suppressed above gas kinetic temperatures of a few hundred K and for dust temperatures above 200-300 K and below 10 K. We highlight the differences between our treatment of the H $_{2}$ formation process and other descriptions in the literature. We also study the relative importance of H $_{2}$ formation on dust grains with respect to molecular hydrogen formation in the gas phase, through the H $^{-}$ route. The ratio of formation rates of these two routes depends to a large part on the dust abundance, on the electron abundance, and also on the relative strength of the FUV (extra-)galactic radiation field. We find that for a cosmological evolution of the star formation rate and dust density consistent with the Madau plot, a positive feedback effect on the abundance of H $_{2}$ due to the presence of dust grains can occur at redshifts $z \geq 3$ . This effect occurs for a dust-to-gas mass ratio as small as 10 $^{- 3}$ of the galactic value.

Molecular hydrogen formation on dust grains in the high redshift universe

Abstract

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