Radio relic discovered in the merger of huge clusters of galaxies

Using ASKAP, a radio interferometer at the Murchison Observatory in Western Australia (ASKAP), an international team of astronomers have discovered radio relics in a converging galactic group known as SPT-CL 2023-5535. This is reported in a research article published on the arXiv repository.

Radio relics are diffuse elongated radio sources of synchrotron origin. They occur in spectacular single or double symmetric arcs at the periphery of galaxy clusters. Astronomers are particularly interested in looking for such sources in merging galaxy clusters, as the number of radio models associated with merging collisions is still small.

SPT-CL 2023-5535 (abbreviated as CL2023) is a massive merging galaxy cluster at a redshift of 0.23 and about 727,000 light-years across. The presence of diffuse radio emission in this cluster was assumed in previous studies. However, due to the insufficient spatial resolution of these observations and the presence of several bright neighboring radio point sources, this hypothesis has not yet been confirmed.

Radio relic in space

The confirmation came recently from a group of astronomers led by Kim Hyun Han of Yonsei University in Seoul, Republic of Korea. Scientists report the discovery of a radio relic in CL2023 as a result of the analysis of deep, high-resolution radio imagery “ASCAP” – Evolutionary Map of the Universe (EMU). The study was complemented by data from the 4-meter Blanco telescope at the Cerro Tololo Inter-American Observatory and NASA’s Chandra X-ray spacecraft.



We report the discovery of a radio relic in the merging cluster SPT-CL 2023-5535 at z = 0.23 from the ASKAP-EMU pilot study 300 sq. Grad (800-1.088 MHz).

Excerpt from original research

According to the study, the relic in CL2023 extends approximately 1.6 million light-years. Scientists have found that the radiation source is located on the western edge of the radio halo. Radio halo are large-scale sources of diffuse radio emission located in the centers of some galaxy clusters.

The relic radio flux density was calculated at about 16.2 mJ, while its extrapolated radio flux density at 1.4 GHz was measured at about 12.0 mJ. It was found that the integrated spectral index of the relic is at the level of -0.76.

In addition, studies have confirmed that CL2023 is indeed a massive system, with its total mass estimated at about 1040 trillion solar masses. It was also found that CL2023 consists of at least three subclusters.

Astronomers have concluded that CL2023 is a post-fusion system in which two of its subclusters may have suffered a major collision between 200 and 300 million years ago.

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