Astronomers have discovered a strange “radio halo” in a huge cluster of galaxies

Radio halos are huge areas of diffuse radio emission.which are usually found in the centers of massive galaxy clustersand which may have a regular morphology that tends to follow the intracluster X-ray emitting medium (ICM).

However, diffuse emissions usually have very low surface brightness, especially at GHz frequencies, making it difficult to detect. Its brightness increases at lower frequencies, indicating the presence of these areas.

Radioelectric halo detected

Now, group of astronomers Under the direction of Sinenhlanhla Precious Sikhosana, University of KwaZulu-Natal, Durban, South Africa. discovered a new radio halo in ACT-CL J0329.2-2330.

(or ACT-CL J0329), a cluster of galaxies with a mass of about 970 billion solar masses, with a redshift of 1.23.

Opening is the result of L-band and UHF observations of this cluster on the MeerKAT radio telescope.as part of the MeerKAT Massive Remote Cluster Study (MMDCS).

“We present MeerKAT’s L-band and UHF observations of ACT-CL J0329.2-2330, a galaxy cluster with az=1.23. Low-resolution images show a radio halo in the cluster. Low-resolution images show a radio halo in the cluster. (…) MeerKAT observations were conducted in L-band with a total over-target time of 3.5 hours, using a discharge rate of 8 seconds and 4096 channels,” the researchers wrote.

By analyzing the images, Sihosana’s team determined extended emission at the center of ACT-CL J0329 with a linear extent of more than 3.59 million light years at 1.28 GHz.. MeerKAT images also show that ACT-CL J0329’s radio halo has a smooth and regular morphology, reflecting thermal bremsstrahlung (radiation produced when electrical charges slow down) from the intracluster medium (ICM).

Based on these results, astronomers classified this emission as a radio halo. The study concluded that the recently discovered radio halo has flux densities of 3.44 and 6.11 mJy in the L and UHF bands., respectively. The integral spectral index of the halo was estimated at 1.3, and its radio power at 4.4 YW/Hz.

ACT-CL J0329 is as bright as halos found in nearby massive galaxy clusters.

These results suggest that The halo of ACT-CL J0329 is as bright as those in nearby massive galaxy clusters.which apparently confirms the fact of a rapid increase in the magnetic field in galaxy clusters at high redshifts.

In his closing remarks The authors of the article emphasized that the spectral index map of ACT-CL J0329 shows discernible vibrations, since the highest values ​​of the spectral index are concentrated in the eastern region. This may indicate that turbulent energy is not dissipated uniformly throughout the halo volume.

Link to news:
Sikhosana S, Hilton M, Bernardi G, et al. MeerKAT survey of massive distant clusters: a radio halo in a massive galaxy cluster at z = 1.23. arXiv (2024).