Extragalactic Abundances of Hydrogen, Deuterium and Helium New Steps, Missteps and Next Steps

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Scientific paper

Estimates of the deuterium abundance in quasar absorbers are reviewed, including a brief account of incorrect claims published by the author and a brief review of the problem of hydrogen contamination. It is concluded that the primordial abundance may be universal with a value (D/H)P ~ 10-4, within about a factor of two, corresponding to $$\Omega _Bh_{0.7}^2$$ ~ 0.02 or eta10 ~ 2.7 in the Standard Big Bang. This agrees with current limits on primordial helium, YP <= 0.243, which are shown to be surprisingly insensitive to models of stellar enrichment. It also agrees with a tabulated sum of the total density of baryons in observed components. Much lower primordial deuterium (~ 2 x 10-5) is also possible but disagrees with currently estimated helium abundances; the larger baryon density in this case fits better with current models of the Lyman-alpha forest but requires the bulk of the baryons to be in some currently uncounted form.

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