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Radio relic discovered in a nearby galaxy cluster

Radio relic discovered in a nearby galaxy cluster

MeerKAT radio contours (magenta) on A2384 XMM-Newton image. Credit: Parekh et al., 2020.

Using the MeerKAT radio telescope in South Africa, an international team of astronomers has discovered a radio relic in a nearby low-mass, fusing galaxy cluster designated A2384. The finding is reported in a research paper published on September 6 on the arXiv pre-print 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 periphery of galaxy clusters. Astronomers are particularly interested in searching for such sources in the fusion of galaxy clusters, as the number of radio relics associated with fusion shocks is still small.

At a redshift of 0.092, the A2384 is a nearby low mass (approximately 261

trillion solar masses), complex galaxy cluster. It consists of two components, designated A2384 (N) and A2384 (S), which show a dense X-ray filament between them, estimated to be about 2.3 million light-years long.

A group of astronomers led by Viral Parekh from Rhodes University in Makhanda, South Africa, observed A2384 with MeerKAT in May 2019. They identified an extended radio source located at the edge of the galaxy cluster that turned out to be a single radio relic.

“In our MeerKAT images, we discovered an extended radio source at the bottom of the A2384 (S) cluster,” the researchers wrote in the newspaper.

The newly found radio source is located perpendicular to the fusion axis A2384 and extends from southeast to northwest. Its dimensions are approx. 2.7 at 0.86 million light-years, and the source’s radio power at 1.4 GHz was measured to be 387 million PW / Hz. Astronomers noted that the geometry, location, and size of this source indicate that it is a radio relic associated with fusion shock and the A2384 cluster.

In addition, the MeerKAT data reveal that the relic in A2384 is a very steep spectrum source between 941-1454 MHz, with a spectral index at a level of approx. -2.5. According to the authors of the paper, this suggests a re-acceleration of the pre-relativistic electrons in the presence of fusion shock.

Trying to explain the origin of this radio relic, astronomers assume that it is most likely the result of shock wave propagation during the passage of the low-mass A2384 (S) cluster through the massive A2384 (N) cluster. This can create a track seen as a hot X-ray filament between the two components of the cluster.

“During the interaction between the clusters, the sub-cluster A2384 (S) has passed through the A2384 (N) and probably removed a large amount of hot gas (and a number of galaxies) from both systems in the direction of the fusion,” the researchers explained.

In addition to the discovery of the radio relic in A2384, Parekh’s team also found a candidate radio comb in the X – ray filament of the cluster. The ridge is relatively small (about 590,000 x 420,000 light-years), and astronomers assume it could be a new class of radio source located between the two components of the A2384.

Radio relic discovered in a merging galaxy cluster

More information:
Parekh et al., MeerKAT’s discovery of a radio relic in the bimodal merging cluster A2384, arXiv: 2009.02724 [astro-ph.GA] arxiv.org/abs/2009.02724

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Citation: Radio relic discovered in a nearby galaxy cluster (2020, September 15) retrieved September 15, 2020 from https://phys.org/news/2020-09-radio-relic-nearby-galaxy-cluster.html

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