Scientists Spot Intergalactic Wind Stripping Falling Galaxies of Star-Forming Gas

Astronomers have provided the first ever direct evidence that an intergalactic "wind" is stripping galaxies of star-forming gas as they fall into clusters of galaxies. The findings may help explain why galaxies found in clusters are known to have relatively little gas and less star formation when compared to non-cluster or "field" galaxies.

In the past, astronomers theorized that as a field galaxy falls into a cluster of galaxies, it hits the cloud of hot gas at the center of the cluster. As the galaxy moves through this intra-cluster medium at thousands of kilometers per second, the cloud acts like a wind and strips away the gas within the galaxy without disturbing its stars, called ram-pressure stripping.

Previous observations have shown indirect evidence of ram-pressure stripping of star-forming gas. Astronomers spotted young stars trailing from a galaxy; the stars would have formed from gas that was newly-stripped from the galaxy.

Now, scientists have seen ram-stripping in action. The researchers used observations of four galaxies, which were stripped of their star-forming gas by this wind. By examining these galaxies, though, the scientists were able to prove that the galaxies had this gas-stripping wind effect in common.

The researchers used optical, infrared and hydrogen-emission data from both the Spitzer and Hubble space telescopes, as well as archival ground-based data.

"For more than 40 years we have been trying to understand why galaxies in dense clusters have so few young stars compared with ones like our Milky Way Galaxy, but now we see the quenching of star formation in action," said George Rieke, one of the researchers, in a news release. "Cutting off the gas that forms stars is a key step in the evolution of galaxies form the early universe to the present."

The findings are published in The Astrophysical Journal.