Heating of the intergalactic medium as a result of structure formation

Abstract

We estimate the heating of the intergalactic medium as a result of shocks arising from structure formation. The heating of the gas outside the collapsed regions, with small overdensities [(nb/nb)<<200] is considered here, with the aid of a Zel'dovich approximation. We estimate the equation of state of this gas, relating the density to its temperature and its evolution in time, considering the shock heating caused by 1σ density peaks as being the most dominant. We also estimate the mass fraction of gas above a given temperature as a function of redshift. We find that the baryon fraction above 106K at z=0 is ~10 per cent. We estimate the integrated Sunyaev-Zel'dovich distortion from this gas at present epoch to be of the order of 10-6.