A Radio and X-ray Study of the Merging Cluster A2319

TL;DR

This study combines radio and X-ray observations of galaxy cluster A2319 to analyze its merging activity, revealing a two-component radio halo and insights into the interactions between thermal and nonthermal gas components.

Contribution

It provides new high-resolution radio and X-ray analysis of A2319, discovering a distinct radio core and examining the origin of the radio halo in merging galaxy clusters.

Findings

Discovery of a 800 kpc radio core with morphology similar to X-ray emission.

Detection of radio emission trailing from the core into the larger halo.

Evidence against a hadronic origin for the cosmic ray electrons in the halo.

Abstract

A2319 is a massive, merging galaxy cluster with a previously detected radio halo that roughly follows the X-ray emitting gas. We present the results from recent observations of A2319 at 20 cm with the Jansky Very Large Array (VLA) and a re-analysis of the X-ray observations from XMM-Newton, to investigate the interactions between the thermal and nonthermal components of the ICM . We confirm previous reports of an X-ray cold front, and report on the discovery of a distinct core to the radio halo, 800 kpc in extent, that is strikingly similar in morphology to the X-ray emission, and drops sharply in brightness at the cold front. We detect additional radio emission trailing off from the core, which blends smoothly into the 2 Mpc halo detected with the Green Bank Telescope (GBT; Farnsworth et al., 2013). We speculate on the possible mechanisms for such a two-component radio halo, with sloshing playing a dominant role in the core. By directly comparing the X-ray and radio emission, we find that a hadronic origin for the cosmic ray electrons responsible for the radio halo would require a magnetic field and/or cosmic ray proton distribution that increases with radial distance from the cluster center, and is therefore disfavored.