An international team, including lead researchers from the University of Minnesota and the South African Radio Astronomy Observatory (SARAO), have released highly detailed images of radio emissions from 115 clusters of galaxies that give new clues to the formation and evolution of galaxies throughout the Universe.
The overview paper for the MeerKAT Galaxy Cluster Legacy Survey (MGCLS) is scheduled for publication in Astronomy & Astrophysics, an international peer-reviewed journal. The findings are accompanied by the public release of a huge trove of curated data now available for astronomers worldwide.
Researchers used SARAO's MeerKAT telescope, located in the Karoo region of the Northern Cape province of South Africa. The observations, amounting to approximately 1000 hours of telescope time, were done in the year following the inauguration of MeerKAT in 2018.
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 in South Africa and SARAO.
University of Minnesota Professor Emeritus Lawrence Rudnick, in the College of Science and Engineering's School of Physics and Astronomy, chaired the Technical Working Group for the survey, which was responsible for providing scientifically useful and reliable data products for the science teams and co-coordinated the work of the multiple science teams that contributed to the survey science.
"With the spectacular new capabilities of the MeerKAT telescope, we were able to lift the veil on processes in clusters of galaxies that were only hinted at before," Rudnick said. "Our common reaction was 'Oh! So that's what it really looks like!'"
The force of gravity has filled the expanding Universe with objects extending over an astounding range of sizes, from comets that are 10 kilometers (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.
This new 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 behavior of cluster plasmas.
Some 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 a variety of 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 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.
"One of the most exciting things for me was seeing a whole new, talented generation of astronomers in South Africa who are advancing the science challenges with which we've struggled for a very long time," Rudnick said.
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. Partial support for Rudnick's efforts is provided by the U.S. National Science Foundation to the University of Minnesota.
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 the 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.
