Contributed Talk - Splinter ISM

Friday, 15 September 2023, 14:00   (H 3006)

Cosmic ray feedback and magnetic dynamos in the interstellar medium

C. Pfrommer, M. Werhahn, R. Pakmor, P. Girichidis
AIP Potsdam, MPA Garching, Universität Heidelberg

The interstellar medium is a dynamic and complex environment that plays a crucial role in shaping the evolution of galaxies and the birth of new stars. The multiphase nature of its components is maintained by interactions through various physical processes, such as ionization, heating, cooling, magnetic fields, and relativistic particle populations (so-called cosmic rays) and it remains a major outstanding challenge to identify the underlying physics. Of particular interest are feedback processes by star formation, supernovae, radiation, and cosmic rays which appear to be critical in obtaining realistic disk galaxies and to slow down star formation to the small observed rates as demonstrated by recent cosmological simulations. However, many of these simulations neglected magnetic fields and cosmic rays. Those are known to provide a pressure support comparable to the thermal gas in our Galaxy and couple dynamically and thermally to the gas, which seriously questions their neglect. After introducing the underlying physical concepts, I will present our recent efforts to model cosmic ray physics and magnetic fields in galaxy formation. In particular, I will identify the different stages of a gravitationally driven magnetic dynamo that grows the field to the observed strengths. I will then explain how cosmic rays interact with and propagate through the magnetized plasma in the interstellar and circumgalactic media and demonstrate that cosmic rays play a decisive role in the formation and evolution of spiral galaxies by providing feedback that regulates star formation and drives gas out in galactic winds. Comparing cosmic ray spectra of electrons and protons to observational data and studying the correlation of the far-infrared emission with the gamma-ray and radio emission from galaxies enables us to test the cosmic ray feedback and dynamo models for the growth of galactic magnetic fields. This argues that a complete understanding of galaxy formation necessarily includes these non-thermal components.