Deuterium in high redshift clouds and baryonic dark matter

Abstract

The recently observed Deuterium abundance in low-metallicity high-redshift hydrogen cloud, which is about ten times larger than that observed in the near interstellar medium, is in excellent agreement with that predicted by the Standard Big Bang Nucleosynthesis theory and the observed abundances of 4 He and 7 Li extrapolated to their primordial values, provided that the cosmic baryon to photon ratio is η = (1.60 ± 0.1) × 10 −10 . This ratio implies a mean cosmic baryon density, in critical density units, of Ω b ≈ (0.0058 ± 0.0007)h −2 , where H 0 ≡ 100h km s −1 Mpc −1 , is the Hubble constant. This mean baryon density is consistent with the observed mean cosmic density of matter visibile in Radio, IR, V, UV or X-ray wave lengths, if h ≈ 0.8. It does not provide any reliable evidence that most of the baryons in the Universe are dark. Moreover, since the dynamics of clusters of galaxies and large scale structures indicate that Ω ≥ 0.10, it does imply that most of the matter in the Universe is non baryonic dark matter.