Megamaser “Nkalakatha” discovered by astronomers using MeerKAT

Press release from SARAO

Artist’s impression of a hydroxyl maser. Inside a galaxy merger are hydroxyl molecules, composed of one atom of hydrogen and one atom of oxygen. When one molecule absorbs a photon at 18cm wavelength, it emits two photons of the same wavelength. When molecular gas is very dense, typically when two galaxies merge, this emission gets very bright and can be detected by radio telescopes such as the MeerKAT. © IDIA/LADUMA using data from NASA/StSci/SKAO/MolView

Using the MeerKAT radio telescope, a team of researchers from the University of the Western Cape, the University of Cape Town, Rhodes University, the South African Radio Astronomy Observatory (SARAO) and the South African Astronomical Observatory (SAAO), together with colleagues from 12 other countries have discovered a powerful megamaser – a radio-wavelength laser indicative of colliding galaxies. This is the most distant such megamaser found so far.

Galaxies are vast islands of matter in the universe. They comprise hundreds of billions of stars, gas and dark matter. When galaxies merge in collisions of cosmic proportions, the gas they contain becomes extremely dense. In particular, this can stimulate hydroxyl molecules, made of one atom of oxygen and one atom of hydrogen, to emit a specific radio signal called a maser (a maser is like a laser but emits radio waves instead of visible light). When that signal is exceedingly bright, it is called a megamaser. “When two galaxies like the Milky Way and the Andromeda Galaxy collide, light beams shoot out from the collision and are visible at cosmological distances.

The OH megamasers act like bright lights that say: here is a collision of galaxies that is making new stars and feeding massive black holes,” explains Prof. Jeremy Darling from the University of Colorado in the United States, a megamaser expert and co-author of the study.

Hydroxyl megamasers emit light at a wavelength of 18cm. This light belongs to the radio part of the electromagnetic spectrum. It is the type of light that the MeerKAT radio telescope in the Karoo’s design enables it to capture exceptionally well.

The Looking at the Distant Universe with the Meerkat Array (LADUMA) team leads one of the big MeerKAT science experiments, which is looking for neutral hydrogen gas in galaxies in one area of the sky, and looking for it very deeply – meaning very far from us, both in space and in time. LADUMA will contribute to our understanding of the universe’s evolution by measuring the neutral hydrogen gas in galaxies from the distant past to now. This is no minor exercise, and so the research team comprises scientists from South Africa, Australia, Chile, France, Germany, India, Italy, Japan, the Netherlands, South Korea, Spain, the UK, and the U“. “LADUMA is probing hydrogen within a single ‘cosmic vuvuzela’ that extends to when the universe was only a third of its present age,” says Associate Professor Sarah Blyth from the University of Cape Town.

The team looks for light with a wavelength of 21cm that the universe’s expansion has stretched to longer wavelengths to look for hydrogen. However, light from other atoms and molecules is also present. In their first observation with MeerKAT, the team detected bright emissions from hydroxyl molecules that had been even more stretched from their original wavelength of 18cm.

Dr Marcin Glowacki, previously a researcher at the Inter-University Institute for Data-Intensive Astronomy (IDIA) and the University of the Western Cape, and now based at the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), led the investigation. He explains, “It’s impressive that in a single night of observations with MeerKAT, we already found a redshift record-breaking megamaser. The full 3000+ hour LADUMA survey will be the most sensitive of its ki”d.” When they saw this signal in the data coming from the telescope and confirmed that it was coming from hydroxyl, the team realised that they had a megamaser on their hands.

The team had to run complex scientific algorithms on large data to make this discovery. This was made possible by the Inter-University Institute for Data Intensive Astronomy (IDIA) research cloud computing facility. This facility exists to help the South African research community do as much science as possible with the MeerKAT and with the upcoming Square Kilometre Array in the future. Indeed, it is one thing to collect a lot of data and another to work with it. Therefore, facilities like IDIA’s are imperative if astronomers are to do as much science as possible with the MeerKAT and with the Square Kilometre Array in the future.

Once the team knew it was a megamaser, they went on to look for its host galaxy. Where was the megamaser coming from? The patch of sky explored by the LADUMA team has undergone observation in X-rays, optical light, and infra-red, so the team could easily identify the host galaxy. The team also knew that such a powerful, distant megamaser needed an excellent nickname and invited the public to offer suggestions. The winning suggestion was “Nkalakata,” an isiZulu word that means “big boss,” which was suggested by Zolile Tibane, a student from Johannesburg who is studying computer science at the University of the Western Cape.

The host galaxy of “Nkalakaha” has a long tail on one side, visible in radio waves. It is about 58 thousand billion billion (58 followed by 21 zeros) kilometres away. This is because the megamaser light was emitted about 5 billion years ago when the universe was only about two-thirds of its current age “. “We have already planned follow-up observations of the megamaser, and as LADUMA progresses, we will make many more discoveries,” notes Dr Glowacki.

This is the first time anyone has detected a megamaser at that distance from its emission at 18cm wavelength. The study’s authors point out that it is not surprising that they found such a bright megamaser, given how powerful the MeerKAT is. Still, the telescope is very new, so this find hopefully is one of many more to come “. “MeerKAT will probably double the known number of these rare phenomena. Experts thought Galaxies merged more often in the past, and the newly discovered OH megamasers will allow us to test this hypothesis,” comments Prof. Darling.

Radio astronomy is entering a fascinating time with the upcoming Square Kilometre Array and its pathfinder telescopes, including MeerKAT. Unplanned discoveries are starting to emerge from the unprecedented amounts of data these instruments collect. And with MeerKAT and IDIA, South Africa is right at the cutting-edge of astronomy.


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