Galaxy mergers could limit star formation

(11 January 2021)

Artist’s impression of ID2299 showing the galaxy, the product of a galactic collision, and some of its gas being ejected by a “tidal tail” as a result of the merger. Credit: ESO/M. Kornmesser.

Our astronomers have looked nine billion years into the past to find evidence that galaxy mergers in the early universe could shut down star formation and affect galaxy growth.

Using a powerful Earth-based telescope they saw that a huge amount of star-forming gas was ejected into the universe by the coming together of two galaxies.

The merger created a new galaxy called ID2299 at a time when the universe was only 4.5 billion years old.

The researchers say that this event, combined with huge star formation in the galaxy’s nuclear regions, could eventually deprive it of the fuel needed to make stars.

This would stop star formation for several hundred million years, effectively halting the galaxy’s development.

Active black holes

Astronomers observe many massive, dead galaxies containing very old stars in the nearby Universe and don’t exactly know how these galaxies have been formed.

Simulations suggest that winds generated by active black holes as they feed, or those created by intense star formation, are responsible for such deaths by expelling the gas from galaxies.

Now our new study offers galaxy mergers as another way of shutting down star formation and altering galaxy growth.

Observational features of winds and “tidal tails” caused by the gravitational interaction between galaxies in such mergers can be very similar.

Galactic winds

But the rate at which the gas is being expelled from ID2299 is too high to have been caused by the energy created by a black hole or starburst as seen in previous studies.

Computer simulations also suggest that black holes can’t kick out as much cold gas from a galaxy as seen in this study.

Therefore, researchers suggest that some past results where galactic winds have been seen as the cause of halting star formation might need to be re-evaluated.

Find out more

• Read the research paper in Nature Astronomy.

• The study was led by Dr Annagrazia Puglisi, a Post-Doc Research Associate in our Centre for Extragalactic Astronomy.

• The research was carried out with the French Alternative Energies and Atomic Energy Commission (CEA) – Saclay, the University of Paris-Saclay and the Lyon Astrophysical Research Centre, France.

• Observations were carried out using the European Southern Observatory’s Atacama Large Millimeter Array (ALMA) telescope, in northern Chile.

• The research was funded in the UK by the Science and Technology Facilities Council, part of UK Research and Innovation.

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