Constraining the Collective Radio Emission of Large Scale Accretion Shocks

TL;DR

This paper investigates how accretion shocks in galaxy clusters contribute to the cosmic radio background, using Coma cluster data and models to set upper limits on their impact across frequencies.

Contribution

It introduces a method to constrain the radio emission from accretion shocks in galaxy clusters, providing upper limits based on Coma cluster observations and shock evolution models.

Findings

Accretion shocks could significantly contribute to the low-frequency cosmic radio background.

At 5 GHz, their contribution is constrained to be less than 2-35%.

The contribution varies depending on the shock evolution models used.

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.