Probing Primordial and Pre-Galactic Lithium with High Velocity Clouds

Abstract

The pre-Galactic abundance of lithium offers a unique window into non-thermal cosmological processes. The primordial Li abundance is guaranteed to be present and probes big bang nucleosynthesis (BBN), while an additional Li component is likely to have been produced by cosmic rays accelerated in large scale structure formation. Pre-Galactic Li currently can only be observed in low metallicity Galactic halo stars, but abundance measurements are plagued with systematic uncertainties due to modeling of stellar atmospheres and convection. We propose a new site for measuring pre-Galactic Li: low-metallicity, high-velocity clouds (HVCs) which are likely to be extragalactic gas accreted onto the Milky Way, and which already have been found to have deuterium abundances consistent with primordial. A Li observation in such an HVC would provide the first extragalactic Li measurement, and could shed new light on the apparent discrepancy between BBN predictions and halo star Li abundance determinations. Furthermore, HVC Li could at the same time test for the presence of non-primordial Li due to cosmic rays. The observability of elemental and isotopic Li abundances is discussed, and candidate sites identified.

10 pages, AASTeX

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Cited by in corpus (8)

• Primordial Nucleosynthesis: from precision cosmology to fundamental physics
• A Bitter Pill: The Primordial Lithium Problem Worsens
• Observation of interstellar lithium in the low-metallicity Small Magellanic Cloud
• Cosmological Cosmic Rays and the observed Li6 plateau in metal poor halo stars
• Implications of a new temperature scale for halo dwarfs on LiBeB and chemical evolution
• Lithium-6 and Gamma Rays: Complementary Constraints on Cosmic-Ray History
• Analytical Models for the Energetics of Cosmic Accretion Shocks, their Cosmological Evolution, and the Effect of Environment
• Galactic Fly-Bys: New Source of Lithium Production