Astronomers have produced a new study demonstrating the best effort yet for measuring the 'quenching' timescale; that is, when a galaxy falls into a cluster, star formation is fairly rapidly shut off.
Led by Ryan Foltz, member of the Spitzer Adaptation of the Red-sequence Cluster Survey, or SpARCS, the study explained how they have been able to measure how quenching varies across 70 per cent of the history of the Universe.
Each galaxy entering a cluster is known to bring some cold gas with it that has not yet formed stars. One possible explanation suggests that before the cold gas can turn into stars, it is "stripped" away from the galaxy by the hot, dense gas already in the cluster, causing star formation to cease.
But until now, the real reason was unknown, as it was very difficult to find distant clusters, and even harder to measure the properties of their galaxies.
We now believe we have a good idea of how star formation stops in the most massive galaxies in clusters
However, the latest survey completed by SpARCS has made a measurement of more than 70 per cent of the history of the Universe, done by pioneering new cluster-detection techniques, which enabled the discovery of hundreds of new clusters in the distant Universe.
Using some of their own newly discovered SpARCS clusters, the fresh study discovered that it takes a galaxy longer to stop forming stars as the Universe gets older: only 1.1 billion years when the Universe was young, 1.3 billion years when the Universe is middle-aged, and five billion years in the present-day.
"Comparing observations of the quenching timescale in galaxies in clusters in the distant universe to those in the nearby universe revealed that a dynamical process, such as gas stripping, is a better fit to the predictions than strangulation or outflows," Foltz explained.
To make this state-of-the art measurement, the SpARCS team required 10 nights of observations with the W. M. Keck Observatory telescopes in Hawaii, and 25 nights of observations with the twin Gemini telescopes in Hawaii and Chile.
"Thanks to the phenomenal investment in our work by these observatories, we now believe we have a good idea of how star formation stops in the most massive galaxies in clusters," added Gillian Wilson, leader of the SpARCS survey and colleague of Foltz.
"There are good reasons, however, to believe that lower-mass galaxies may quench by a different process. That is one of the questions our team is working on answering next."
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