Radio relic detected in a merged galaxy cluster

Using the Australian Square Kilometer Array Pathfinder (ASKAP), an international team of astronomers has detected a radio relic in a fused galaxy cluster known as SPT-CL 2023-5535. The discovery is reported in a research paper published July 16 in the arXiv preprint repository.

Radio relics are diffuse, elongated radio sources of synchrotron origin. They occur in the form of spectacular single or double symmetrical arcs at the peripheries of galaxy clusters. Astronomers are especially interested in looking for such sources to merge galaxy clusters, since the number of radio relics associated with fusion crashes is still small.

SPT-CL 2023-5535 (CL2023 for short) is a cluster of massive fusion galaxies with a redshift of 0.23, about 727,000 light years in size. The presence of diffuse radio broadcasts in this group was suggested by previous studies. However, due to insufficient spatial resolution of these observations and the existence of several bright neighboring radio point sources, this hypothesis has not yet been confirmed.

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

“Here, we report the discovery of a radio relic in the SPT-CL 2023-5535 fusion group at z = 0.23 from the ASKAP-EMU 300 sq. Deg pilot survey (800-1,088 MHz),” the astronomers wrote in the document. .

According to the study, the radio relic in CL2023 spans about 1.6 million light-years in the north-south orientation from the group. The source was found to be located on the western edge of a halo radius, coinciding with the intragroup gas, stretched east-west from CL2023. The radio halo is around 1.6 by 3.2 million light years in size.

The relic radio flux density was calculated at approximately 16.2 mJy, while its radio flux density extrapolated to 1.4 GHz was measured at approximately 12.0 mJy. The relic’s integrated spectral index was found to be at a level of -0.76.

Furthermore, the investigation confirmed that CL2023 is indeed a massive system as its total mass was estimated to be about 1,040 trillion solar masses. CL2023 was also found to consist of at least three subgroups.

Astronomers concluded that, as the results show, CL2023 is a post-merger system, where its two subgroups could have suffered a major collision between 200 and 300 million years ago.

“The current orientation of the CL2023 relic suggests that the merger may be occurring in the east-west direction, implying that the relic is the result of the collision between the middle and eastern subgroups,” the authors of the article wrote.

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