Cosmic Ray Coupling and Subgrid Modeling in the CGM

          @misc{ pirsa_PIRSA:25070045,
            doi = {10.48660/25070045},
            url = {https://pirsa.org/25070045},
            author = {Butsky, Irina},
            keywords = {Cosmology},
            language = {en},
            title = {Cosmic Ray Coupling and Subgrid Modeling in the CGM},
            publisher = {Perimeter Institute},
            year = {2025},
            month = {jul},
            note = {PIRSA:25070045 see, \url{https://pirsa.org}}
          }
          

Abstract

Despite its vast extent—spanning hundreds of kiloparsecs beyond the galactic disk—the circumgalactic medium (CGM) is shaped by microphysical processes operating on much smaller scales. One key example is the coupling between cosmic rays and gas. Under the right conditions, cosmic rays can dominate the pressure support in the CGM of low-redshift L* galaxies. However, this coupling depends sensitively on AU-scale magnetic field fluctuations—well below the resolution limit of modern galaxy-scale simulations. In this talk, I will highlight recent theoretical developments in cosmic-ray transport and their implications for CGM pressure profiles. I’ll also introduce CGSM, a new subgrid model designed to represent unresolved cold gas structures in hydrodynamic simulations, and discuss its potential to bridge the gap between microphysics and galaxy evolution.