In recent years, there has been growing awareness that a large reservoir of hitherto "missing" baryons — enough to close the missing baryon problem on galactic scales — exists in the circumgalactic medium (CGM), extending from beyond the visible stellar component out to the virial radius. However, many interesting puzzles have emerged from CGM observations, such as the origin of multiphase gas and the nature of highly-ionized ions around star-forming galaxies. Most theoretical models and simulations failed to reproduce these observations. In this talk, I will discuss how cosmic rays (CRs) can fundamentally modify the structure of virial shocks and the physical states of the multiphase CGM in galaxy halos, which provides possible explanations for existing puzzles. I will also present preliminary results of the hybrid magnetohydrodynamic-particle-in-cell simulations of CR-dust coupling, where the CR gyro-radius on AU scales is fully resolved.

Suoqing Ji is a Sherman Fairchild fellow in theoretical astrophysics at the California Institute of Technology. He obtained his Ph.D. in physics from UC Santa Barbara in 2018. His research interests include magnetohydrodynamics, turbulence, hydrodynamic and thermal instabilities, cosmic rays, etc., and their application in the circumgalactic medium and stellar physics.