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Large Turbulent Gas Reservoirs around Galaxies

Thanks to the ALMA European interferometer in Chile, an international team involving IRFU has detected ionized CH+ molecules in distant galaxies for the first time. Their observations reveal the unsuspected existence of large turbulent reservoirs of gas surrounding these young galaxies. The findings explain the persistently high star formation rate observed in galaxies known as
 "starburst galaxies".
Published on 4 September 2017

Most galaxies that can be observed today were formed when the universe was between one and two billion years old. In theory, this process is governed by the influx of primordial matter into the galaxies and the ejection of matter via the explosions of massive stars (supernovae) located outside of the galaxies.

The Atacama Large Millimeter/submillimiter Array (ALMA) has allowed the scientists to observe intense CH+ emissions in six distant galaxies of the early universe. Their estimates indicate that the CH+ reservoirs extend over volumes that are larger than the galaxies themselves and that they sometimes contain several times the mass of gases of these galaxies. Highly reactive and therefore unstable, the molecule CH+ is an energy tracer on a galactic scale. The powerful winds resulting from the explosions of stars carry large amounts of energy, generating turbulent movements within large gas reservoirs located on the periphery of galaxies.

According to IRFU researcher Frédéric Bournaud, "this discovery challenges a fundamental theoretical point according to which the material ejected during the supernovae is lost for the original galaxy. It's actually the opposite—these winds partly supply nearby reservoirs and bring turbulence in them, which in turn fosters the formation of new generations of stars."

One of the assets of this scenario is that it justifies why young starburst galaxies have a star formation rate sometimes more than a hundred times higher than current galaxies, and why they continue to form stars after hundreds of millions of years.

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