Intergalactic winds slow star formation

Cosmic winds remove gas from galaxies, preventing the birth of new stars

NGC 4522, in the Virgo Cluster, has a wake of gas and dust being blown from the galaxy.

Credit: Suresh Sivanandam; Dunlap Institute for Astronomy & Astrophysics

As star forming galaxies fall into clusters, their gas is ripped out by intergalactic winds, recent studies have shown. The observations hope to explain why cluster galaxies have much less gas when compared to those found in isolation.

Galaxies in clusters form stars at a significantly slower rate than non-cluster cousins, known as field galaxies. This is because they contain much less gas than field galaxies, meaning fewer stellar nurseries and fewer new stars being born.

Researchers theorised that as a galaxy falls into a cluster it collides with a cloud of hot gas at the centre. As the galaxy moves through the cloud it creates a wind, which blows away the gas but leaves stars undisturbed. The process is known as ram-pressure stripping.

In recent optical, infrared and hydrogen-emission observations made with the Spitzer and Hubble space telescopes, the team observed streams of gas being left behind by galaxies as they fell into clusters. While previous research had shown that the tenuous atomic hydrogen gas surrounding a galaxy is removed by ram-pressure, it was thought that the dense clouds of molecular hydrogen at the core of galaxies would be less susceptible.

“However, we found that the molecular hydrogen gas is also blown from the in-falling galaxy,” says Suresh Sivanandam of the Dunlap Institute at the University of Toronto, “much like smoke blown from a candle being carried into a room.”

These latest observations show trails of the hydrogen gas itself trailing behind the galaxy as it moves through space. The findings prove the long held theory that pressure stripping is responsible for cluster galaxies being so gas poor, resulting in the lack lustre star formation seen in these bodies.

“Seeing this stripped molecular gas is like seeing a theory on display in the sky,” says Marcia Rieke, from the University of Arizona. “Astronomers have assumed that something stopped the star formation in these galaxies, but it is very satisfying to see the actual cause.”


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