Speaker
Description
Cosmic rays (CRs) play crucial roles in various astrophysical environments in the present Universe. They can penetrate deep into dense molecular clouds, altering their ionization degree and influencing star formation. Additionally, CRs exert pressure on galactic gas and contribute to driving galactic winds. However, their role in the early Universe remains poorly understood. Since CRs are expected to be accelerated in supernova remnants of the first stars, they are likely to affect the galactic and intergalactic environments in the early Universe.
In this study, we propose a novel CR heating mechanism and investigate its impact on the intergalactic medium (IGM) at redshift $z \sim 10$. As CRs escape from a galaxy, they carry an electric current, which induces a return current of thermal electrons to maintain current neutrality. Since collisions between thermal electrons and thermal ions are not negligible on cosmological timescales, the return current induces Joule heating. We also consider electron-neutral collisions and evaluate the heating rate by this mechanism. Furthermore, we compare our proposed mechanism with other CR heating processes and the heating by X-rays, which is conventionally considered the dominant heating source of the IGM at $z \sim 10$. By solving the evolution equations of temperature and ionization degree simultaneously, we predict the IGM temperature achieved by these heating mechanisms. Our results suggest that the proposed CR heating mechanism could be a dominant process in determining the IGM temperature at $z \sim 10$. Finally, we discuss the observability of CR heating signatures in future 21-cm line radio observations.
