Constraining the Collective Radio Emission of Large Scale Accretion Shocks

Abstract

Accretion of gas onto already virialized structures like galaxy clusters should give rise to accretion shocks which can potentially accelerate cosmic rays. Here, we use the radio emission detected from Coma cluster and models of evolution of cosmic accretion shocks, to constrain the possible contribution of unresolved galaxy clusters to the cosmic radio background. We assume that Coma is a typical galaxy cluster and that its entire radio emission is produced by cosmic rays accelerated in accretion shocks, making our prediction an upper limit. Our models predict that at lower frequencies accretion shocks can have a potentially large contribution to the cosmic radio background, while on larger frequencies, e.g. 5 GHz, their contribution must be lower than < 2-35%, depending on the models of evolution of accretion shocks that we use.