A distant radio mini-halo in the Phoenix galaxy cluster

Abstract

We report the discovery of extended radio emission in the Phoenix cluster (SPT-CL J2344-4243, z=0.596) with the GMRT at 610 MHz. The diffuse emission extends over a region of at least 400-500 kpc and surrounds the central radio source of the Brightest Cluster Galaxy, but does not appear to be directly associated with it. We classify the diffuse emission as a radio mini-halo, making it the currently most distant mini-halo known. Radio mini-halos have been explained by synchrotron emitting particles re-accelerated via turbulence, possibly induced by gas sloshing generated from a minor merger event. Chandra observations show a non-concentric X-ray surface brightness distribution, which is consistent with this sloshing interpretation. The mini-halo has a flux density of $17\pm 5$ mJy, resulting in a 1.4 GHz radio power of ($10.4\pm 3.5)\times 10^{24}$ W Hz${}^{-1}$. The combined cluster emission, which includes the central compact radio source, is also detected in a shallow GMRT 156 MHz observation and together with the 610 MHz data we compute a spectral index of $-0.84\pm 0.12$ for the overall cluster radio emission. Given that mini-halos typically have steeper radio spectra than cluster radio galaxies, this spectral index should be taken as an upper limit for the mini-halo.

5 pages, 2 figures, 1 table. Accepted for publication in ApJL

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• Multiwavelength radio observations of a Brightest Cluster Galaxy at z=1.71: Detection of a modest Active Galactic Nucleus and evidence for extended star formation
• Clusters of galaxies and the cosmic web with SKA
• Probing the origin of diffuse radio emission in the cool-core of the Phoenix galaxy cluster
• Discovery of a circularly symmetric extended diffuse radio emission around an elliptical galaxy with the VLA FIRST survey
• Extended radio emission in the galaxy cluster MS 0735.6+7421 detected with the Karl G. Jansky Very Large Array
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• Chasing ICM cooling and AGN feedback from the macro to the meso scales in the galaxy cluster ZwCl 235
• Discovery of Radio Jets in Phoenix Galaxy Cluster Center
• Cooling rate and turbulence in the intracluster medium of the cool-core cluster Abell 2667
• Deciphering the ultra-steep spectrum diffuse radio sources discovered in the cool-core cluster Abell~980