Astronomers detect corona in giant galaxy cluster

An international team of astronomers conducted radio observations of a giant galaxy cluster called ACT-CL J0329.2-2330 and detected a new radio halo in the cluster. The findings were reported in a research paper posted on a preprint server on April 5 arXiv.

Radio haloes are huge diffuse radio emission regions that usually appear in the centers of giant galaxy clusters. They show regular shapes and often track the intracluster medium (ICM) of X-ray emissions. However, diffuse emissions often have very low surface brightness, especially at GHz frequencies, which makes them difficult to detect. Their brightness increases at lower frequencies, revealing the presence of these regions.

Now, a team of astronomers led by Sinenhlanhla Precious Sikhosana of the University of KwaZulu Natal in Durban, South Africa, has discovered a new corona in the galaxy ACT-CL J0329.2-2330 (or ACT-CL J0329 for short). The cluster has a mass of approximately 970 megasolar masses and a redshift of 1.23. The discovery was the result of L-band and UHF-band observations of the cluster by the MeerKAT radio telescope as part of the MeerKAT Massive Distant Cluster Survey (MMDCS).

“In this letter, we present the results of MeerKAT L and UHF band observations of ACT-CL J0329.2-2330, a galaxy cluster at z=1.23. Low-resolution images reveal the corona in this cluster .

By analyzing MeerKAT images, Sikhosana’s team determined the extended emission from the center of ACT-CL J0329, with a maximum linear size of 3.59 million light-years at 1.28 GHz. MeerKAT images also show that the corona in ACT-CL J0329 has a smooth, regular morphology that tracks thermal Bremsstrahlung radiation from the intracluster medium (ICM).

Based on these results, astronomers classified this emission as corona, meaning it is the highest redshift halo ever detected.

The study found that the flux densities of the newly discovered corona in the L and UHF bands were 3.44 and 6.11 mJy respectively. The halo’s combined spectral index was calculated to be 1.3, while its radio power was estimated to be 4.4 YW/Hz.

These results show that the halos in ACT-CL J0329 are as bright as those found in nearby giant galaxy clusters, which seems to confirm the presence of rapid magnetic field amplification in galaxy clusters at high redshifts.

In their concluding remarks, the authors emphasized that the spectral index plot of ACT-CL J0329 shows significant fluctuations, as steeper spectral index values ​​are concentrated in the eastern region. This may indicate that the turbulent energy is not dissipated uniformly in the halo volume.

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