Electron heating in non-relativistic perpendicular shocks

An on-going question about astrophysical collisionless shocks is whether electrons and ions reach different temperatures downstream of a supernova remnant shock or whether they equilibrate. We investigate the electron heating mechanism in collisionless, non-relativistic, quasi-perpendicular, electron-ion shocks from first principles. We perform fully kinetic, 2D particle-in-cell simulations to follow the shock formation until the downstream steady state is reached. Our simulations are performed for a range of Alfvénic Mach numbers (M_A) from 2 to 50, and of sonic Mach numbers (M_S) from 2 to 36. The two species tend to reach equipartition as M_S approaches unity, independently of M_A value. For larger M_S, electron-ion temperature ratio weakly depends on M_A and falls in the range 0.1-0.5, much larger than the number of the order of mass ratio expected in the absence of collisionless heating. Electrons gain energy in the shock foot due to the electric field associated with the cross-shock potential. The shock transition region becomes filamentary for larger M_A, indicating that Weibel instability may be responsible for electron scattering and isotropization. We have checked the convergence of our results by performing a parametric study on mass ratio and particles per cell number.