Large MeerKAT data release reveals beautiful new cosmic puzzles

An international team led by a young South African researcher has just announced a comprehensive overview paper for the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). The paper to be published in the Astronomy & Astrophysicsjournal presents some exciting, novel results, and is accompanied by the public release of a huge trove of curated data now available for astronomers worldwide to address a variety of challenging questions, such as those relating to the formation and evolution of galaxies throughout the universe.

Using the South African Radio Astronomy Observatory’s MeerKAT telescope, located in the Karoo region of the Northern Cape province, this first observatory-led survey demonstrates MeerKAT’s exceptional strengths by producing highly detailed and sensitive images of the radio emission from 115 clusters of galaxies. The observations, amounting to approximately 1000 hours of telescope time, were done in the year following the inauguration of MeerKAT in 2018.

“In those days we were still characterizing our new telescope, while developing further capabilities required by numerous scientists,” said Dr. Sharmila Goedhart, SARAO head of commissioning and science operations. “But we knew that MeerKAT was already very capable for studies of this sort, and we observed galaxy clusters as needed to fill gaps in the observing schedule.”

This was only the start. More than two years of work followed to convert the raw data into radio images, using powerful computers, and to perform scientific analysis addressing a variety of topics. This was done by a large team of South African and international experts led by Dr. Kenda Knowles of Rhodes University and SARAO. Dr. Michelle Lochner, Senior Lecturer at UWC was also part of this project.

MeerKAT view of a complex network of radio filaments and diffuse structure, spanning more than half a million light-years, related to a galaxy affected by dynamical activity in the nearby galaxy cluster Abell 85. Adapted from K. Knowles et al., “The MeerKAT Galaxy Cluster Legacy Survey. I. Survey Overview and Highlights” (Astronomy & Astrophysics, in press). Image credit: SARAO.

The force of gravity has filled the expanding universe with objects extending over an astounding range of sizes, from comets that are 10 km (one thirty-thousandth of a light-second) across, to clusters of galaxies that can span 10 million light-years. These galaxy clusters are complex environments, host to thousands of galaxies, magnetic fields, and large regions – millions of light-years across – of extremely hot (millions of degrees) gas, electrons and protons moving close to the speed of light, and dark matter. Those ‘relativistic’ electrons, spiraling around the magnetic fields, produce the radio emission that MeerKAT can ‘see’ with unprecedented sensitivity, opening new horizons for the deeper understanding of these structures. Thus MeerKAT, particularly when adding information from optical and infrared and X-ray telescopes, is exceptionally well-suited to studying the interplay between the components that determine the evolution of galaxy clusters, the largest structures in the universe held together by gravity.

We live in an ocean of air, but we can’t see it directly. However, if it’s filled with smoke or dust or water droplets, then suddenly we can see the gusts and swirls, whether they’re a gentle breeze or an approaching tornado. Similarly, the motions of the X-ray-glowing plasma in galaxy clusters are usually hidden from us. Radio emission from the sprinkling of relativistic electrons in this plasma can uncover the dramatic storms in clusters, stirred up when clusters collide with each other, or when jets of material spew out of supermassive black holes in the centers of galaxies.

The MGCLS paper just accepted for publication presents more than 50 newly discovered such patches of emission. Some of them we can understand and others remain a mystery, awaiting advances in our understanding of the physical behavior of cluster plasmas. A few examples are shown here, some associated with the bright emission from so-called ‘radio galaxies,’ powered by the jets of supermassive black holes. Others are isolated features, illuminating winds and intergalactic shock waves in the surrounding plasma. Other types of science enriched by the MGCLS include the regulation of star formation in galaxies, the physical processes of jet interactions, the study of faint cooler hydrogen gas – the fuel of stars – in a variety of environments, and yet unknown investigations to be facilitated by serendipitous discoveries.

The MGCLS has revealed several new systems hosting faint sources on large scales. Here we see radio evidence of a powerful merger taking place between two or more massive groups of gas and galaxies. These structures (a so-called ‘halo’ near the center and two ‘relics’ surrounding it are seen in the galaxy cluster MCXC J0352.4-7401) trace the positions and strengths of cosmic magnetic fields and electron populations travelling near the speed of light. This MeerKAT image spans approximately 10 million light-years at the distance of the cluster, and is sprinkled with point-like radio emission from even more distant Milky Way-like galaxies. Adapted from K. Knowles et al., “The MeerKAT Galaxy Cluster Legacy Survey. I. Survey Overview and Highlights” (Astronomy & Astrophysics, in press). Image credit: SARAO.

The MGCLS has produced detailed images of the extremely faint radio sky, while surveying a very large volume of space. “That’s what’s already enabled us to serendipitously discover rare kinds of galaxies, interactions, and diffuse features of radio emission, many of them quite beautiful,” explained Dr. Knowles. But this is only the beginning.

A number of additional studies delving more deeply into some of the initial discoveries are already underway by members of the MGCLS team. Beyond that, the richness of the science resulting from the MGCLS is expected to grow over the coming years, as astronomers from around the world download the data from the SARAO MeerKAT archive, and probe it to answer their own questions.

Two giant radio galaxies (more than one million light-years from end to end) at the center of a large group of galaxies in the cluster Abell 194, revealing the presence of relatively narrow magnetic filaments in the region, as well as complex interactions between the radio emission from the two galaxies. The MeerKAT radio image is shown in orange, with an optical image dominated by normal galaxies shown in white. Adapted from K. Knowles et al., “The MeerKAT Galaxy Cluster Legacy Survey. I. Survey Overview and Highlights” (Astronomy & Astrophysics, in press). Image credit: SARAO, SDSS.

The Paper

Knowles et al., “The MeerKAT Galaxy Cluster Legacy Survey. I. Survey Overview and Highlights“, accepted for publication in Astronomy & Astrophysics.

The Collaboration

It takes more than a village to create this astronomical bonanza. MeerKAT, the South African SKA precursor that will be integrated into the SKA1-Mid telescope in the coming decade, was conceived, designed, and built over 15 years through the dedicated effort of hundreds of people in South African research organizations, industry, universities, and government. Some 100 of these colleagues that built, operate and maintain MeerKAT are co-authors of the MGCLS paper.

A team of 40 South African and international scientists was involved in the detailed analysis that is presented in the paper and associated data release. They represent 19 institutions, including 10 in South Africa: University of KwaZulu-Natal, Rhodes University, South African Radio Astronomy Observatory, University of the Witwatersrand, University of Pretoria, University of Cape Town, North-West University, University of the Western Cape, African Institute for Mathematical Sciences, Inter-University Institute for Data Intensive Astronomy; U.S. National Radio Astronomy Observatory, University of Minnesota, Italian National Institute for Astrophysics, York University, University of Hamburg, University of Nigeria, U.S. Naval Research Laboratory, University of Bonn, Sapienza University of Rome.

The Telescope and Observatory

The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation.

Originally posted on the SARAO website