ATCA 16 cm Observation of CIZA J1358.9-4750: Implication of Merger Stage and Constraint on Non-Thermal Properties

TL;DR

This study uses 16 cm radio observations to investigate the merging galaxy cluster CIZA J1358.9-4750, finding no significant diffuse emission and constraining the non-thermal properties and magnetic field strength related to merger shocks.

Contribution

First radio observation of CIZA J1358.9-4750 constraining non-thermal emission and magnetic fields in a merging galaxy cluster with implications for shock properties.

Findings

No significant diffuse radio emission detected.

Upper limit on radio power is below expected from empirical relations.

Constraints on magnetic field strength below 0.68 microGauss.

Abstract

We report the Australia Telescope Compact Array 16 cm observation of CIZA J1358.9-4750. Recent X-ray studies imply that this galaxy cluster is composed of merging, binary clusters. Using the EW367 configuration, we found no significant diffuse radio emission in and around the cluster. An upper limit of the total radio power at 1.4 GHz is $\sim 1.1 \times 10^{22}$ Watt/Hz in $30$ square arcminutes which is a typical size of radio relics. It is known that an empirical relation holds between the total radio power and X-ray luminosity of the host cluster. The upper limit is about one order of magnitude lower than the power expected from the relation. Very young ($\sim 70$ Myr) shocks with low Mach numbers ($\sim 1.3$), which are often seen at an early stage of merger simulations, are suggested by the previous X-ray observation. The shocks may generate cosmic-ray electrons with a steep energy spectrum, which is consistent with non-detection of bright ($>10^{23}$ Watt/Hz) relic in this 16 cm band observation. Based on the assumption of energy equipartition, the upper limit gives the magnetic-field strength below $0.68f(D_{\rm los}/{\rm 1~Mpc})^{-1}(\gamma_{\rm min}/200)^{-1}$ $\mu$G, where $f$ is the cosmic-ray total energy density over the cosmic-ray electron energy density, $D_{\rm los}$ is the depth of the shock wave along the sightline and $\gamma_{\rm min}$ is the lower cutoff Lorentz factor of the cosmic-ray electron energy spectrum.