UP researcher uses MeerKAT to discover large gas-rich galaxy group hiding in plain sight

A study led by a University of Pretoria (UP) master’s student using South Africa’s MeerKAT telescope has led to the discovery of a group of 20 galaxies. This large galaxy group is likely the most neutral hydrogen gas-rich group ever discovered, and it is the first time this group has been identified, despite residing in a very well-studied area of the sky.

The research was led by Shilpa Ranchod, an MSc student in the University of Pretoria’s (UP) Department of Physics, supervised by Professor Roger Deane, Founder of the UP Radio Astronomy Research Group, and now Extraordinary Professor. “The distribution of neutral hydrogen gas in these galaxies has revealed interesting, disturbed morphologies suggesting that these galaxies are group members and are being influenced by their cosmic neighbours in the group,” Ranchod said. “For example, we found an interacting pair of galaxies that will potentially merge to form a new galaxy with a completely transformed appearance.”

Ranchod added that the MeerKAT observations show a galaxy group in its early stages of formation, which is extremely rare. “Through this, we are able to understand how galaxy groups are assembled and evolve. This group inhabits an area of sky that has been studied by many other telescopes, but the group structure has been revealed for the first time due to MeerKAT’s excellent sensitivity.”

Most star-forming galaxies are embedded within a cloud of cold neutral hydrogen gas, which acts as the raw fuel from which stars can eventually form. This gas is extremely faint, and can only be detected in radio wavelengths. It is diffuse, and extends beyond the visible part of the galaxy. By observing this hydrogen gas, astronomers are able to understand the evolutionary processes that take place in galaxies.

The majority of galaxies in the Universe reside in groups. However, it is rare to detect a group with such a large number of group members with so much neutral hydrogen. This suggests that the group is still in the process of assembly, as it has not undergone evolutionary processes that would remove this gas from the galaxies.

This galaxy group was discovered by the MeerKAT International Gigahertz Tiered Extragalactic Exploration (MIGHTEE) survey. It is one of the large survey projects in progress using South Africa’s MeerKAT telescope, and involves a team of South African and international astronomers.

The MeerKAT radio telescope in the Northern Cape, South Africa’s precursor to the Square Kilometre Array (SKA), aims to answer fundamental questions about the formation and evolution of galaxies. Its exceptional sensitivity provides astronomers with further insight into the drivers of galaxy evolution.

“MeerKAT continues to impress us with new discoveries, thanks to some brilliant South African engineers who have delivered a world-leading instrument,” said Professor Deane. “To see our bright young students take hold of the scientific opportunities this presents and carry out internationally acclaimed research is both a rewarding and essential step as we plan ahead toward the Square Kilometre Array era."

Ranchod’s galaxy group was found in a survey that produces hundreds of terabytes of data, which are processed via the cloud computing facility hosted by the inter-university Institute of Data-Intensive Astronomy (IDIA), a partnership between the Universities of Pretoria, Cape Town, and the Western Cape.

Professor Chris Theron, Head of UP’s Department of Physics, noted that, "By equipping smart and inquisitive students with the hardware and software tools required to carry out big data research, we open enormous discovery potential. In the Department of Physics, we endeavour to do exactly that." Prof Theron represents UP on the inter-university Institute for Data-Intensive Astronomy management team.

This discovery has been published in the Monthly Notices of the Royal Astronomical Society. Click here to read the publicly available pre-print

Shilpa Ranchod

July 6, 2021

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  • Shilpa Ranchod
    Shilpa Ranchod graduated from the University of Pretoria with an MSc which focused on detecting distant neutral hydrogen (HI) using MeerKAT, through gravitational lensing and HI spectral stacking, as well as HI in galaxy groups in the nearby Universe. MeerKAT is a world-class radio telescope located in the Northern Cape and South Africa’s precursor to the Square Kilometre Array.

    She began her PhD at the University of the Witwatersrand and will be continuing her PhD studies at the Max Planck Institute for Radio Astronomy in Bonn, Germany, where she will study the polarisation properties of extragalactic sources using MeerKAT. She completed her BSc (Hons) at the University of Cape Town under the National Astrophysics and Space Science Programme (NASSP).

    How did you first get interested in radio astronomy?
    I was first exposed to radio astronomy in the first year of my undergraduate degree, when we visited the South African Radio Astronomy Observatory in Cape Town. There I learned about MeerKAT, which was still being built at the time, and the amazing potential for discovery using this new instrument.

    How does it feel to be one of the few women in this field?
    In my experience, there are many very accomplished women in this field. A lot has been done to ensure that more women are pursuing careers in astronomy, and I would not like to take away from that.

    For someone so young (25), it’s impressive that you’ve made such a big discovery. Where would you like your research to take you in the future?
    I hope to publish many more papers on extragalactic radio science, as well as continue to work with large international collaborations. The discoveries resulting from MeerKAT are so impressive, which makes me excited to do science with the Square Kilometre Array (SKA) in the future.

    Why does your research matter?
    There are many gaps in our understanding of how galaxies are formed, and what drives their evolution. The study of galaxies in different environments – for example, groups and clusters – helps us understand the role of this in galaxy evolution. The detection of a galaxy group through neutral hydrogen emission is important, as the extended nature of the gas can reveal how galaxies interact with each other and their environment.

    What do you enjoy doing in your spare time?
    I enjoy doing yoga, crocheting, spending time out in the sun, and hanging out with family and friends.

    How does this discovery alter our understanding of the skies?
    This discovery is particularly exciting because we have discovered a galaxy group in its early stages of formation. This is a unique snapshot of a galaxy group in its evolutionary timeline. Our discovery, along with other observations and simulations of massive galaxy groups, will provide a complete picture of how these groups, and the galaxies within them, form and evolve.

    What advice would you give young South African learners who are interested in astronomy?
    Maths, physics and programming can be challenging, but if you are passionate, work hard and persevere, there are so many opportunities for exciting discoveries, particularly in South Africa and with MeerKAT. From my experience so far, this makes astronomy as a career extremely rewarding.
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