Resistive Magnetic Field Generation at Cosmic Dawn

Relativistic charged particles (CRs for cosmic rays) produced by supernova explosion of the first generation of massive stars that are responsible for the reionization of the universe escape into the intergalactic medium, carrying an electric current. Charge imbalance and induction give rise to a return current, , carried by the cold thermal plasma which tends to cancel the CR current. The electric field, , required to draw the collisional return current opposes the outflow of low-energy CRs and ohmically heats the cold plasma. Owing to inhomogeneities in the resistivity, η( T ), caused by a structure in the temperature, T , of the intergalactic plasma, the electric field possesses a rotational component which sustains Faraday's induction. It is found that a magnetic field is robustly generated throughout intergalactic space at a rate of 10 −17 to 10 −16 G Gyr −1 , until the temperature of the intergalactic medium is raised by cosmic reionization. The magnetic field may seed the subsequent growth of magnetic fields in the intergalactic environment. The role of CR-driven instabilities is discussed, and nonlinear effects are briefly considered.