Cosmic rays, lithium abundance and excess entropy in galaxy clusters

Abstract

We consider the production of ${}^6$Li in spallation reactions by cosmic rays in order to explain the observed abundance in halo metal-poor stars. We show that heating of ambient gas by cosmic rays is an inevitable consequence of this process, and estimate the energy input required to reproduce the observed abundance of ${}^6$Li/H$\sim 10^{-11}$ to be of order a few hundred eV per particle. We draw attention to the possibility that this could explain the excess entropy in gas in galaxy groups and clusters. The evolution of ${}^6$Li and the accompanying heating of gas is calculated for structures collapsing at the present epoch with injection of cosmic rays at high redshift. We determine the energy required to explain the abundance of ${}^6$Li at $z\sim 2$ corresponding to the formation epoch of halo metal-poor stars, and also an increased entropy level of $\sim 300$ keV cm${}^2$ necessary to explain X-ray observations of clusters. The energy budget for this process is consistent with the expected energy output of radio-loud AGNs, and the diffusion length scale of cosmic-ray protons responsible for heating is comparable to the size of regions with excess entropy. We also discuss the constraints imposed by the extragalactic gamma-ray background.

5 pages, 1 Figure, Accepted for publication in MNRAS (Letters)

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Cited by in corpus (11)

• Primordial Nucleosynthesis: from precision cosmology to fundamental physics
• Feedback Heating by Cosmic Rays in Clusters of Galaxies
• Big Bang Nucleosynthesis with Bound States of Long-lived Charged Particles
• The cosmic 6Li and 7Li problems and BBN with long-lived charged massive particles
• Polycyclic aromatic hydrocarbon processing by cosmic rays
• Gravitino Dark Matter and the Cosmic Lithium Abundances
• Population III Generated Cosmic Rays and the Production of Li6
• Light Element Production in the Circumstellar Matter of Energetic Type Ic Supernovae
• Limits on the AGN activities in X-ray underluminous galaxy groups
• On the DM interpretation of the origin of non-thermal phenomena in galaxy clusters
• Cosmic ray heating of intergalactic medium: patchy or uniform?