Cosmic Rays as Drivers and Diagnostics of Galaxy Evolution

Abstract: Cosmic rays interact with astrophysical systems across a vast range of scales, from dense molecular clouds to circum-galactic gas flows. As active agents capable of depositing energy and momentum into their surroundings, cosmic rays can shape galaxy evolution in multiple ways. They also produce observational signatures across the electromagnetic spectrum and through multi-messenger channels. These signatures can be used to constrain cosmic-ray effects, and also to probe the structure, dynamics, and evolution of different components of galaxy ecosystems imprinted by their formation histories. In this talk, I will discuss how cosmic rays shape, and are shaped by, galaxy evolution.

Within galaxies, hadronic and leptonic cosmic rays can alter the conditions for star formation, regulate baryon cycling, and generate observable signatures in the sub-mm band, X-rays, gamma-rays, and neutrinos. On larger scales, the process of galaxy assembly and growth can itself be shaped by externally supplied cosmic rays. These may be entrained into cold inflows, where they can heat and disrupt fragile stream-halo interfaces to selectively modify the gas supply to massive galaxies. Finally, long-lived cosmic-ray sources, such as millisecond pulsars in globular clusters, may serve as complementary high-energy signatures of the galaxy assembly process, linking high-energy emission from galaxies to their merger and accretion history, structure, and the spatial build-up of galactic bulges and halos. Together, these perspectives illustrate how multi-wavelength and multi-messenger observations can extend studies of galaxies beyond traditional electromagnetic tracers, and unveil the intricate coupled evolution of cosmic rays, baryons, and magnetic fields.