An international team, led by Rhodes University Research Fellow, Dr Kenda Knowles, has just announced a comprehensive overview paper for the MeerKAT Galaxy Cluster Legacy Survey (MGCLS), accompanied by the public release of a vast trove of curated data that astronomers worldwide can use to address a variety of challenging questions relating to the formation and evolution of galaxies throughout the universe.
The paper, "The MeerKAT Galaxy Cluster Legacy Survey. I. Survey Overview and Highlights", which has been accepted for publication in the Astronomy & Astrophysics journal, presents some exciting and novel results.
"I'm very excited to see the impact MeerKAT can have in the global astronomy space and eager to see where the beautiful data will take us to better understand the many different components of our Universe," said Dr Knowles, who is the lead author of the paper. "The complexity that is being revealed in radio galaxy structures, and how common this complexity actually seems to be, is very thrilling."
Dr Mpati Ramatsoku, Research Fellow at Rhodes University, who also contributed to the paper, has been similarly impressed by the "sheer number of completely new and complex galaxy structures that have been revealed" by the data and how the survey "opens up a fresh perspective on how galaxies form, live and evolve".
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.
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.
"The Rhodes Centre for Radio Astronomy Techniques & Technologies has been immensely supportive and has provided all facilities which allowed us to make important contributions to this work," Dr Ramatsoku explained.
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, spiralling around the magnetic fields, produce the radio emission that MeerKAT can see. Thus MeerKAT, particularly when adding information from optical and infrared and X-ray telescopes, is exceptionally well-suited to studying the interplay between these 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 centres of galaxies. The MGCLS paper 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 behaviour of cluster plasmas.
Some examples are 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 various environments, and yet unknown investigations to be facilitated by serendipitous discoveries.
The MGCLS has produced detailed images of the extremely faint radio sky while surveying a substantial 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.
"MeerKAT is making massive contributions to radio astronomy, but we have lots still to do. Data like this provides a lot of scope for training up the next generation of South African astronomers," she said.
Several 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 worldwide download the data from the SARAO MeerKAT archive and probe it to answer their questions.
K. Knowles et al., "The MeerKAT Galaxy Cluster Legacy Survey. I. Survey Overview and Highlights", accepted for publication in Astronomy & Astrophysics.
MeerKAT was conceived, designed, and built over 15 years through the dedicated effort of hundreds of people in South African research organisations, 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 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; US National Radio Astronomy Observatory, University of Minnesota, Italian National Institute for Astrophysics, York University, University of Hamburg, University of Nigeria, US 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, a facility of the National Research Foundation, an agency of the Department of Science and Innovation.