Is Deuterium in High Redshift Lyman Limit Systems Primordial?

Abstract

Detections of deuterium in high redshift Lyman limit absorption systems along the line of sight to QSOs promise to reveal the primordial deuterium abundance. At present, the deuterium abundances (D/H) derived from the very few systems observed are significantly discordant. Assuming the validity of all the data, if this discordance does not reflect intrinsic primordial inhomogeneity, then it must arise from processes operating after the primordial nucleosynthesis epoch. We consider processes which might lead to significant deuterium production/destruction, yet allow the cloud to mimick a chemically unevolved system. These processes include, for example, anomalous/stochastic chemical evolution and D/{${}^4$He} photo-destruction. In general, we find it unlikely that these processes could have altered significantly (D/H) in Lyman limit clouds. We argue that chemical evolution scenarios, unless very finely tuned, cannot account for significant local deuterium depletion since they tend to overproduce ${}^{12}$C, even when allowance is made for possible outflow. Similarly, D/{${}^4$He} photo-destruction schemes engineered to locally produce or destroy deuterium founder on the necessity of requiring an improbably large $\gamma$-ray source density. Future observations of (D/H) in Lyman limit systems may provide important insight into the initial conditions for the primordial nucleosynthesis process, early chemical evolution, and the galaxy formation process.

16 pages, Latex (aasms4.sty)

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• The Deuterium Abundance Towards Q1009+2956
• Big-bang Nucleosynthesis Enters the Precision Era
• The Deuterium to Hydrogen Abundance Ratio Towards a Fourth QSO: HS0105+1619
• Review of Big Bang Nucleosynthesis and Primordial Abundances
• What Is The BBN Prediction for the Baryon Density and How Reliable Is It?
• A High Deuterium Abundance at z=0.7
• Deuterium abundances
• Neutrino Production of Deuterium in Supermassive Stars and Possible Implications for Deuterium Detections in Ly-Limit Systems
• Deuterium at high redshift: primordial or evolved ?
• Cosmological Deuterium Production in Non-Standard Scenarios
• Production of 2H, 3He, and 7Li from Interactions Between Jets and Clouds