Groningen Astronomers solve the mystery of cold gas in hot quasars

A team of astronomers from the University of Groningen, including Peter Barthel and Pece Podigachoski, have solved the fifty-year-old mystery of why cold gas flows out of hot quasars. New observations indicate that the cold gas probably forms during the rapid formation of stars in the host galaxy of the quasar, and is expelled by stellar explosions. The astronomers’ article has been accepted for publication in the journal Astrophysical Journal Letters.

A quasar is the brightly shining nucleus of a galaxy. Quasars (galactic nuclei) were common in the early universe and shine brightly because the supermassive black hole in the centre sucks in material, which then begins to smoulder. This heat emission is typical of quasars.

In 1966, much to their surprise, astronomers discovered that quasars contain not only hot but also cold gas. In addition, this gas turned out to be fast-moving. For fifty years, astronomers have been trying to work out where the cold gas comes from, how much of it there is and why it is able to reach speeds of thousands of kilometres per second.

Peter Barthel (Kapteyn Institute, University of Groningen): ‘We also wanted to know how important these gas winds are within the host galaxy of the quasar, and their net effect on the early universe. As these galaxies ultimately evolve into galaxies like our Milky Way, we are keen to understand the process.’

An international team of astronomers decided to use the Herschel Space Observatory to examine several quasars more closely. Their observations revealed that the cold gas mainly occurs in quasars with a high rate of star formation. Barthel: ‘Rapid star formation in quasar host galaxies somehow seems to be connected with these cold gas super winds.’

Barthel developed this hypothesis with his PhD student Pece Podigachoski and colleagues Belinda Wilkes for the Harvard College Observatory and Martin Haas from the University of Bochum. They suspect that the winds are driven by starbursts that occur when lots of stars are formed rapidly.

It is possible that the stellar winds form a natural obstacle to the formation of large numbers of stars and larger galaxies. Barthel: ‘Theoretically, galaxies could be enormous, but in practice, this just doesn’t seem to occur.’

Article
Starburst-driven superwinds in quasar host galaxies . Peter Barthel, Pece Podigachoski, Belinda Wilkes & Martin Haas. Accepted for publication in Astrophysical Journal Letters ( free preprint ).