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Galaxies have bipolar gas outflows far into intergalactic space

For the first time, astronomers have observed in three dimensions that gas from spiral galaxies is blown upwards and downwards at high speed, far out of the galaxy. They thereby confirm the theory of galaxy evolution: that star-forming galaxies create intergalactic gas flows by discharging gas along the poles. 'Thanks to this study, we can no longer ignore bipolar winds,' says Leiden astronomer Joop Schaye. The astronomers publish their findings in Nature.

In models describing the formation of galaxies, gas flows are important. Galaxies grow by the incursion of gas from their surroundings. Growth, the idea goes, is inhibited by young stars and supermassive black holes blowing gas far back into space via shock waves. What exactly happens is unknown, but without strong gas currents, galaxies would grow far too heavy.

Researchers have now convincingly demonstrated that galactic winds reach far beyond the galaxies. They did so using the MUSE instrument on the Very Large Telescope in Chile. They studied the signal from rarefied magnesium gas around nearly two hundred, distant, spiral galaxies. In half of these galaxies, they look at the edge of the disc. In the other half, they see the disc as a circle.

Gas flows (red) near spiral galaxies (white)

Gas up to tens of thousands of light years from the system

In the group of galaxies where the astronomers looked at the edge, they found that the gas flows perpendicularly upwards and downwards. 'We can see the gas up to tens of thousands of light years from the galaxy and it is moving through intergalactic space at hundreds of kilometres per second,' says first author Yucheng Guo (Université de Lyon, France).

'It is a real milestone for me that we now finally see a picture of intergalactic gas flows around ordinary galaxies,' says Leiden astronomer Joop Schaye. He co-authored the study and has been researching galactic winds and gas in the space between galaxies for years. 'Until now, observations were difficult to interpret, but thanks to this study, we can no longer ignore bipolar winds.'

Now that astronomers have mapped average gas flows and velocities, they can test and adjust their computer simulations of galaxy evolution. This is important because it will make it clearer how galaxies grow.

Scientific article

Bipolar outflows out to 10 kpc for massive galaxies at redshift z ≈ 1. Door: Yucheng Guo et al. In: Nature, 7 december 2023. [original | preprint (pdf)]

This article appeared as a press release on the website of de Nederlandse Onderzoekschool voor Astronomie (NOVA)
Image: HST/ESO/VLT/MUSE/Yucheng Guo et al. 
Header: ESA

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