ATCA 16 cm Observation of CIZA J1358.9-4750: Implication of Merger Stage and Constraint on Non-Thermal Properties
2016
We report the Australia Telescope Compact Array 16 cm observation of CIZA J1358.9-4750. Recent X-ray studies imply that this
galaxy clusteris 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-rayelectrons 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-raytotal energy density over the
cosmic-rayelectron energy density, $D_{\rm los}$ is the depth of the shock wave along the sightline and $\gamma_{\rm min}$ is the lower cutoff
Lorentz factorof the
cosmic-rayelectron energy spectrum.
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