Radio remnants discovered in a nearby galaxy cluster

Miracat Radio Controls (Magenta) on the A2384 XMM-Newton image. Credit: Parekh et al., 2020.

An international team of astronomers has detected a radio remnant in the nearby, low-mass, merged galaxy cluster A2384, using the Miracat radio telescope in South Africa. Information about this discovery has been published in a research paper, published on September 6 in the ArtX Pre-Print Repository.

Spreading radio residues are long radio sources of synchrotron origin. They occur as spectacular single or double symmetric arcs at the periphery of galaxy clusters. Astronomers are particularly interested in discovering such sources in merging galaxy clusters, as the number of radio residues associated with the merger shock is still small.

At redshift of 0.092, A2384 is a near, low-mass (about 261 trillion solar masses), complex group of galaxies. It consists of two components, designated by A2384 (N) and A2384 (S), estimated to be approximately 2.3 million light years long, showing a dense X-ray filament between them.

A group of astronomers led by Viral Parekh of Rhodes University in Makhanda, South Africa, observed the A2384 with Meerat in May 2019. They identified an extended radio source located at the edge of a galaxy cluster that is a single radio remnant.

The researchers wrote in the paper, “In our Mercut images, we discovered an extended radio source beneath the A2384 (S) cluster.”

The newly found radio source A2384 is located perpendicular to the merger axis, which extends from southeast to northwest. Its amplitude is approximately 2.7 to 0.86 million light years and the radio power of the source at 1.4 GHz was measured to be 387 million PW / Hz. Astronomers noted that the geometry, location, and shape of this source indicate that it is a radio residue associated with merger shocks and the A2384 cluster.

Furthermore, the Meerkat data suggests that residues in A2384 are a very stable spectrum source with a spectral index between 941–1454 MHz at a level of about −2.5. This, according to the authors of the paper, suggests re-acceleration of pre-relative electrons in the presence of merger shock.

Trying to explain the origin of this radio residue, astronomers believe that it is a shock wave during the passage of a low-mass A2384 (S) cluster through a massive A2384 (N) cluster. Is the result of the spread of. This can create a mark seen between the two components of the cluster as a warm X-ray filament.

“During cluster interactions, sub-cluster A2384 (S) passed through A2384 (N) and is likely to divert large amounts of hot gas (and many galaxies) from both systems towards the merger,” the researchers explained. .

In addition to radio residue detection in A2384, Parekh’s team also found a candidate radio ridge in the X-ray filament of the cluster. The ridge is relatively small (about 590,000 by 420,000 light years) and astronomers believe it may be a new class of radio source located between the two components of the A2384.

Radio residue found in a merged galaxy cluster

more information:
Radio residue meerkat discovered in Parekh et al., Bimodal merging cluster A2384, arXiv: 2009.02724 [astro-ph.GA]

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Quotes: Radio remnants discovered in the nearby galaxy cluster (2020, 15 September) recovered from on 15 September 2020

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