|List of EVOLI's Presentation(s) ( Updated 20/01/2011 11:58:49 )|
|Precise if your presentation is oral or a poster :||Poster|
|Title of your presentation :||Lithium production by cosmological cosmic rays during Milky Way evolution.|
|Authors: C. Evoli, S. Salvadori and A. Ferrara (SISSA, Trieste)
The 6Li abundances observed in metal-poor halo stars (MPHSs) exhibit a metallicity plateau at $[6Li/H] = -11.2$.
However, standard BBN models coupled with WMAP5 cosmological parameters predict a 6Li abundance about 1000 times smaller. Such discrepancy can be cured by either modifying well-settled BBN models or by invoking a subsequent mechanism that acts during Galaxy evolution.
A promising mechanism is the production of 6Li by spallation of cosmological cosmic rays (CCR) accelerated by
supernovae (SNe) during the early formation of the Milky Way. In fact, 6Li can be synthesized after the BBN epoch
by fusion reactions (alpha+alpha -> 6Li), when high-energy cosmic ray particles collide with ambient gas particles.
In particular, this reaction is very efficient at high redshift and is independent of metallicity.
Starting from a recent model of Milky Way (MW) evolution we follow the star formation and supernova history, and the chemical enrichment of the MW throughout its hierarchical merger tree, matching simultaneously several of the observed properties of the MW, and the Metallicity Distribution Function (MDF) of Galactic halo stars.
We then study the resulting nucleosynthesis if most of the cosmic-rays produced were injected from Galactic substructures in which SNe exploded and escaped into the galactic medium (GM) interacting with He nuclei. We find that realistic and properly constrained models of Galaxy evolution can hardly explain the observed value of 6Li abundance and, in particular, cannot account for the observed 6Li flat metallicity distribution.
Thus, it seems that to explain the observed plateau it is necessary to invoke a pre-galactic 6Li production by some
yet unknown mechanism.