Energetic Winds Blow From The Triangle Galaxy

October 25, 2022

(News from Nanowerk) Galaxies are systems of interacting stars and interstellar gases. Observations show that galaxies today form fewer stars than in the past. Since cold gas is needed to form stars, models link the deceleration of star formation and the observed evolution of galaxies to galactic winds blowing cold gas away.

Galactic winds originate in the disks of galaxies and extend to the halo and intergalactic medium, however, their origin is still debated. Supernova explosions and active galactic nuclei (AGNs) can drive powerful winds, but their role in star formation is complicated by the fact that gas from their winds can fall back onto the galactic disc and trigger the formation of new ones. stars.

Through new radio observations with the Karl G. Jansky Very Large Array, an international team of researchers has found evidence of cosmic rays as an alternate agent of galactic winds in our neighboring galaxy M33 in the constellation Triangle (The Triangle) at a distance of 2.7 million light years from Earth. This galaxy is smaller than the Milky Way by about 23 times in mass.

Artist’s rendering of cosmic ray-driven winds (blue and green) superimposed on an optical image of the triangular galaxy M33 (red and white) observed with the VLT Survey Telescope at ESO’s Paranal Observatory in Chile. (Image: Institute for Research in Basic Sciences (IPM) and European Southern Observatory)

Cosmic rays are high-energy particles that can travel at speeds comparable to the speed of light. They can increase pressure in the interstellar medium, drive outflows and alter galaxy-wide structures. Previous studies had indicated the importance of cosmic ray-driven winds in the formation of bubbles at scales of a few thousand light-years in the Milky Way and the Andromeda galaxy.

“This is the first time we have found evidence of such winds in a low-mass star-forming spiral galaxy such as M33,” says Fatemeh Tabatabaei, the lead researcher on this research. “This evidence emerged from a contradiction when we discovered that cosmic ray electrons are more energetic in regions where the magnetic field is also stronger. In a strong magnetic field, cosmic ray electrons are expected to lose energy to stronger synchrotron radiation. Tabatabaei conducted his research thesis (thesis: 2008) at the Max Planck Institute for Radio Astronomy (MPIfR) under the supervision of Rainer Beck, co-author of the present study (Royal Astronomical Society Monthly Notices, “Cloud-scale radio records of star formation and feedback in Triangle Galaxy M 33: VLA observations”).

This paradox can be solved by taking into account the structure of the magnetic field. In star-forming regions, the magnetic field is amplified due to turbulent gas movements by the impact of a dynamo mechanism that converts kinetic energy into magnetic energy. The resulting field is highly entangled. “The dynamo is a powerful mechanism that operates everywhere in the Universe: in stars, planets, galaxies, and even huge intergalactic gas clouds,” explains Rainer Beck.

“This tangled structure of the magnetic field helps cosmic rays disperse before they lose their energy due to synchrotron cooling in the magnetic field. These high-energy cosmic rays can then easily mix with background gas and plasma and create high-pressure regions in the disk. The resulting pressure imbalance between the disk and the outer layers of the halo causes winds,” explains Fatemeh Tabatabaei.

The present study shows that cosmic ray-driven winds may play a role in most galaxies, especially those with relatively low mass but active star formation, such as M33, much more frequent systems than massive galaxies. Therefore, in principle, cosmic ray-driven winds may also have played an important role in removing the gas in earlier times, as they were even stronger due to higher star-forming activities.

“In order to confirm and extend these findings to earlier epochs of the Universe, radio observations of more distant galaxies are needed, which becomes feasible with future sensitive radio telescopes such as the Next Generation Very Large Telescope and the Observatory. SKA”, concludes Karl Menten, Director of the MPIfR and head of its millimeter and submillimeter research department, also co-author of the article.