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Star Formation Reduced in Galactic Groups

By Stephen Luntz

Galaxies in groups lose hydrogen gas as they move through the intergalactic medium, making it harder for them to form stars.

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The process has previously been known in large galactic clusters, but has now been extended to galaxies in groups similar to our own.

Galaxies are formed out of huge clouds of gas, much of which gradually forms into stars. However, in clusters and groups of galaxies there is intergalactic medium stretching between the galaxies.

Within clusters, which can have thousands of galaxies, the intergalactic medium becomes very hot. “When a galaxy moves through this hot medium, most of its hydrogen gas can be easily removed,” says Dr Luca Cortese of Swinburne University’s Centre for Astrophysics and Supercomputing.

The intergalactic medium in small groups of galaxies is much cooler, and was not expected to have the capacity to remove gas from the disks of galaxies. Nevertheless, when Cortese and Dr Barbara Catinella used the Arecibo Telescope to examine galaxies around 500 million light years away they found that these grouped galaxies still have less hydrogen gas than those flying solo.

“It is unclear which physical process is responsible for the observed gas deficit in group galaxies. The milder intergalactic medium in groups might not suffice,” says Catinella. She hopes the completion of the Square Kilometre Array will allow us to answer this question.

Catinella says that if the intergalactic medium is not hot enough to strip the gas it is...

The full text of this article can be purchased from Informit.