From 10 K to 10 TK: Insights on the Interaction Between Cosmic Rays and Gas in Starbursts*

摘要

Recent work has both illuminated and mystified our attempts to understand cosmic rays (CRs) in slarburst galaxies. I discuss my new research exploring how CRs interact with the ISM in starbursls. Molecular clouds provide targets for CR protons to produce pionic gamma rays and ioni/ation, but those same losses may shield the cloud interiors. In the densest molecular clouds, gamma rays and ~(26)A1 decay can provide ionization, at rales up to those in Milky Way molecular clouds. I then consider the free-free absorption of low frequency radio emission from starbursts, which I argue arises from many small, discrete H II regions rather than from a "uniform slab" of ionized gas, whereas synchrotron emission arises outside them. Finally, noting that the hoi superwind gas phase fills most of the volume of starbursts, I suggest that it has turbulent-driven magnetic fields powered by supernovae, and that this phase is where most synchrotron emission arises. 1 show how such a scenario could explain the far-infrared radio correlation, in context of my previous work. A big issue is that radio and gamma-ray observations imply CRs also must interact with dense gas. Understanding how this happens requires a more advanced understanding of turbulence and CR propagation.