Large MeerKAT data release reveals beautiful new cosmic puzzles

An international team led by a young South African researcher has announced a comprehensive overview paper for the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). The paper to be published in the Astronomy & Astrophysics journal presents some exciting, novel results. Furthermore, it is accompanied by the public release of curated data now available for astronomers worldwide. The astronomers can use the data to address various challenging questions, including galaxy formation and evolution.

The observatory-led survey demonstrates MeerKAT’s exceptional strengths by producing detailed and sensitive images of radio emission from 115 galaxy clusters. Furthermore, MeerKAT made the observations in 2019, following its inauguration in 2018. This consequently amounts to approximately 1000 hours of telescope time. “In those days, we were still characterising our new telescope while developing further capabilities required by numerous scientists,” said Dr Sharmila Goedhart. Dr Sharmila Goedhart is SARAO’s head of commissioning and science operations. She added that “ we knew MeerKAT was already very capable for studies of this sort, and we observed galaxy clusters to fill gaps in the observing schedule.”

More than two years of work followed to convert the data into radio images, using powerful computers for scientific analyses. Dr Kenda Knowles of Rhodes University and SARAO led the team, including several South African and international experts.

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.

Relativistic electrons that spiral around stellar magnetic fields produce the radio emission that MeerKAT detects. MeerKAT makes the detections because of its unprecedented sensitivity, opening new horizons for a deep understanding of these structures. Thus MeerKAT is suitable for studying the interplay between the components that determine the evolution of galaxy clusters. This is particularly when adding information from optical and infrared, and X-ray telescopes. The MGCLS paper presents more than 50 newly discovered such patches of emission. While we can understand some of them, others remain a mystery, awaiting advances in understanding cluster plasmas’ physical behaviour. A few examples are 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. 

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 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 highly faint radio sky while surveying a very large volume of space. “That’s what’s enabled us to discover rare kinds of galaxies, interactions, and diffuse features of radio emission,” explained Dr Knowles. But this is only the beginning. Many additional studies delving more deeply into some of the initial discoveries are already underway by members of the MGCLS team. Beyond that, SARAO expects the richness of the science resulting from the MGCLS to grow over the coming years. This is as astronomers download the data from the SARAO MeerKAT archive, probing it to answer their questions.

Two giant radio galaxies (more than one million light-years from end to end) at the centre 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 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.