Cosmological Implications of the Uncertainty in H−Destruction Rate Coefficients

In primordial gas, molecular hydrogen forms primarily through associativedetachment of H- and H, thereby destroying the H-. The H- anion can also bedestroyed by a number of other reactions, most notably by mutual neutralizationwith protons. However, neither the associative detachment nor the mutualneutralization rate coefficients are well determined: both may be uncertain byas much as an order of magnitude. This introduces a corresponding uncertaintyinto the H2 formation rate, which may have cosmological implications. Here, weexamine the effect that these uncertainties have on the formation of H2 and thecooling of protogalactic gas in a variety of situations. We show that theeffect is particularly large for protogalaxies forming in previously ionizedregions, affecting our predictions of whether or not a given protogalaxy cancool and condense within a Hubble time, and altering the strength of theultraviolet background that is required to prevent collapse.Comment: 40 pages, 17 figures, AASTex. Submitted to Ap