MeerKAT Measures the Fuel Reserves of Galaxies in the Past

An example of an HI-rich spiral galaxy. The image is an RGB image built using data from the Hyper Suprime-Cam at Subaru Telescope (Mauna Kea Observatory, Hawaii), and represents the light emitted from stars in the galaxy. The white contour shows the extension of the HI emission (as revealed by MeerKAT), which goes well beyond the stars and consists in a diffuse cloud of gas. The project has studied how the amount of gas changes with the amount of stars and with age of the universe. Credit: Francesco Sinigaglia/MIGHTEE

A global team of astronomers have measured the fuel for star formation in galaxies as they were four billion years ago using the MeerKAT radio telescope to observe neutral hydrogen gas, the most abundant element in the universe, and the material from which stars are formed. Observation of distant galaxies was one of the prime design drivers for MeerKAT, built and run by the South African Radio Astronomy Observatory (SARAO).

PhD student Francesco Sinigaglia led the measuring work under the supervision of Associate Professor Giulia Rodighiero, both at the University of Padova, Italy, and South African astronomers, Dr Ed Elson at the University of the Western Cape (UWC) and Prof. Mattia Vaccari at the Inter-University Institute for Data Intensive Astronomy (IDIA). The radio data come from MIGHTEE (MeerKAT International GHz Tiered Extragalactic Exploration), a MeerKAT large survey project. 

For the first time, the hydrogen gas measurement could be made for galaxies of different sizes and star formation activity to see how the fuel content relates to other observable properties of galaxies 4 billion years in the past, to compare with what we see in galaxies in the present day.

The researchers expected the amount of gas in galaxies to be more considerable 4 billion years ago than it is today and that galaxies would consume their gas in the star formation process. However, the gas reservoirs of such distant galaxies are similar to those observed in galaxies closer to us. This shows that galaxies can replenish their reservoirs of fuel for star formation by collecting gas from their surroundings. 

The work was possible due to the sensitivity of MeerKAT, the large number of galaxies observed, and the excellent additional data at optical wavelengths. The collaboration between Italy and South Africa has been recently strengthened by bilateral projects such as RADIOSKY2020, co-funded by the Italian Ministero degli Affari Esteri e della Cooperazione Internazionale (MAECI) and the South African National Research Foundation (NRF), says Prof. Vaccari, who is coordinating South Africa’s participation in the RADIOSKY2020 project.

Lead author Francesco Sinigaglia said, “We were thrilled to exploit the potential of MeerKAT to improve our understanding of the cold gas in distant galaxies. We believe this study represents a decisive step forward in the field, as it delivers new pieces of information on hydrogen in galaxies, never obtained before.”

The project involves researchers and students from five South African institutions in the MIGHTEE collaboration and is an international project involving astronomers worldwide. “It is exciting to be a part of such a large, international project as part of PhD studies,” says Sambatriniaina Rajohnson, a PhD student at the University of Cape Town who took part in the project.

The observations from MeerKAT were processed at the Ilifu cloud computing facility set up by the Inter-University Institute for Data Intensive Astronomy, a partnership between the University of Cape Town, the University of the Western Cape, and the University of Pretoria.

According to Dr Bradley Frank, Associate Director for Astronomy Computing at IDIA and the co-chair of MIGHTEE-HI, “The data taught us a lot about the processing challenges involved and was an important testbed for coordinating science projects. Francesco’s science result is the perfect validation for our processing strategy and teamwork, providing an exciting glimpse of the future of MIGHTEE.” 

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