Published in Space Science Reviews, Volume 134, Issue 1-4, pp. 141-153, 2008.
astro-ph/0801.1008

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EQUILIBRATION PROCESSES IN THE WARM-HOT INTERGALACTIC MEDIUM

A.M. Bykov 1, F.B.S. Paerels 2 and V. Petrosian 3


1 A.F. Ioffe Institute of Physics and Technology, St. Petersburg, 194021, Russia
E-mail: byk@astro.ioffe.ru
2 Columbia Astrophysics Laboratory, Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027
E-mail: frits@astro.columbia.edu
3 Department of Physics, Stanford University, Stanford, CA 94305
E-mail: vahe@astronomy.stanford.edu


Abstract. The Warm-Hot Intergalactic Medium (WHIM) is thought to contribute about 40-50% to the baryonic budget at the present evolution stage of the universe. The observed large scale structure is likely to be due to gravitational growth of density fluctuations in the post-inflation era. The evolving cosmic web is governed by non-linear gravitational growth of the initially weak density fluctuations in the dark energy dominated cosmology. Non-linear structure formation, accretion and merging processes, star forming and AGN activity produce gas shocks in the WHIM. Shock waves are converting a fraction of the gravitation power to thermal and non-thermal emission of baryonic/leptonic matter. They provide the most likely way to power the luminous matter in the WHIM. The plasma shocks in the WHIM are expected to be collisionless. Collisionless shocks produce a highly non-equilibrium state with anisotropic temperatures and a large differences in ion and electron temperatures. We discuss the ion and electron heating by the collisionless shocks and then review the plasma processes responsible for the Coulomb equilibration and collisional ionisation equilibrium of oxygen ions in the WHIM. MHD-turbulence produced by the strong collisionless shocks could provide a sizeable non-thermal contribution to the observed Doppler parameter of the UV line spectra of the WHIM.


Key words: intergalactic medium - shock waves - galaxies: clusters: general


Table of Contents

INTRODUCTION

WHIM HEATING AND ION TEMPERATURE EVOLUTION
Collisionless shock heating of the ions
Collisionless heating of the electrons

COULOMB RELAXATION OF TEMPERATURES IN THE WHIM
Relaxation of the ion temperature anisotropy
Relaxation of the ion and electron temperatures
Effect of postshock plasma micro-turbulence on the line widths

IONISATION STATE OF THE WHIM

CONCLUSIONS

REFERENCES

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