We discussed some specific features of the WHIM heating processes by collisionless plasma shocks driven by gravitationally accelerated flows in the LSS structure formation scenario.
Collisionless shock heating of ions in the WHIM results in a highly non-equilibrium initial state with a strongly anisotropic quasi-Maxwellian ion distribution just behind a very thin magnetic ramp region. The ion temperatures just behind the shock depend on the ion atomic weight, the charge state and the shock magnetic field inclination. The ion temperatures could decline from a simple linear scaling with the ion mass providing an excessive heating of heavy ions.
The ion and electron temperatures relax to the equilibrium state through Coulomb collisions in a layer of the depth Neq ~ 1016 v74 cm-2 behind a shock of velocity v7.
Strong collisionless plasma shocks with an efficient Fermi acceleration of energetic particles can generate strong MHD waves in the downstream region that will result in a non-thermal broadening of the emission/absorption lines in the observed WHIM spectra.
Acknowledgements. The authors thank ISSI (Bern) for support of the team "Non-virialized X-ray components in clusters of galaxies". A.M.B. thanks M. Yu. Gustov for his help with hybrid shock simulations, he acknowledges the RBRF grant 06-02-16844 and a support from RAS Presidium Programs. A support from NASA ATP (NNX07AG79G) is acknowledged.