The galactic winds produced by stellar explosions in galaxies enable them to receive and exchange matter with their external environment.
An international team of researchers headed, on the French side, by the CNRS and l’Université Claude Bernard Lyon 1, has mapped a galactic wind for the first time. They achieved this by using the MUSE instrument from the Very Large Telescope at the ESO.
This exceptional observation has been explained in a study published on September 16th, 2021, in MNRAS. The observation helps unravel where some of the universe’s missing matter is situated and to visualize how a nebula is formed around a galaxy.
Galaxies are similar to islands of stars in the universe and constitute ordinary or baryonic matter. This matter includes not only elements from the periodic table but also dark matter, the composition of which is still unknown.
About 80% of the baryons constituting the normal matter of galaxies are missing, which is a major hurdle in understanding how galaxies form. Different models of the universe explain that galactic winds formed by stellar explosions expelled baryons from galaxies into intergalactic space.
The international research team successfully created a detailed map of the galactic wind that induces exchanges between a young galaxy under formation and a nebula (a cloud of gas and interstellar dust), by using the MUSE instrument.
The researchers chose to observe galaxy Gal1 as it is very close to a quasar, acting as a “lighthouse” for the researchers by guiding them toward the area of study. They also intended to observe a nebula surrounding this galaxy. However, the success of this observation was first unpredictable. This is because the luminosity of the nebula was unknown.
Thanks to the ideal positioning of the galaxy and the quasar and the finding of gas exchange caused by galactic winds, the researchers were able to create a unique map. This allowed the first observation of a nebula that was forming and simultaneously emitting and absorbing magnesium — some of the missing baryons of the universe — with the Gal1 galaxy.
Although normal matter nebula of this kind is known in the near universe, their occurrence around young galaxies under formation had only been hypothesized.
Thus, researchers discovered some of the missing baryons of the universe, confirming that 80% – 90% of normal matter can be found outside of galaxies. This observation will help expand models explaining the evolution of galaxies.
Zabl, J., et al. (2021) MusE GAs FLOw and Wind (MEGAFLOW) VIII. Discovery of a MgII emission halo probed by a quasar sightline. Monthly Notices of the Royal Astronomical Society. doi.org/10.1093/mnras/stab2165.