Detection of a radio bridge in Abell 3667

TL;DR

This paper reports the first high-significance detection of a radio bridge in Abell 3667, linking the NW relic to the cluster center, and provides evidence for turbulence-related diffuse synchrotron emission associated with a major merger shock.

Contribution

It presents the first clear detection of a radio bridge connecting a cluster relic with the core, linked to turbulence and shock activity, using multi-frequency radio observations.

Findings

Detection of a radio bridge connecting relic and cluster center

Alignment of radio emission with X-ray diffuse tail

Magnetic field strength estimated at 2.2 microGauss

Abstract

We have detected a radio bridge of unpolarized synchrotron emission connecting the NW relic of the galaxy cluster Abell 3667 to its central regions. We used data at 2.3 GHz from the S-band Polarization All Sky Survey (S-PASS) and at 3.3 GHz from a follow up observation, both conducted with the Parkes Radio Telescope. This emission is further aligned with a diffuse X-ray tail, and represents the most compelling evidence for an association between intracluster medium turbulence and diffuse synchrotron emission. This is the first clear detection of a bridge associated both with an outlying cluster relic and X-ray diffuse emission. All the indicators point toward the synchrotron bridge being related to the post-shock turbulent wake trailing the shock front generated by a major merger in a massive cluster. Although predicted by simulations, this is the first time such emission is detected with high significance and clearly associated with the path of a confirmed shock. Although the origin of the relativistic electrons is still unknown, the turbulent re-acceleration model provides a natural explanation for the large-scale emission. The equipartition magnetic field intensity of the bridge is B_eq = 2.2 +/- 0.3 \mu G. We further detect diffuse emission coincident with the central regions of the cluster for the first time.