On the supernova heating of the intergalactic medium

We present estimates of the energy input from supernovae (SNe) into the int ergalactic medium using (i) recent measurements of Si and Fe abundances in the intracluster medium (ICM), and (ii) self-consistent gasdynamical simula tions that include processes of cooling, star formation, SNe feedback and a multiphase model of the interstellar medium. We estimate the energy input from observed abundances using two different assumptions: (i) spatial unifo rmity of metal abundances in the ICM, and (ii) radial abundance gradients. We show that these two cases lead to energy input estimates which are diffe rent by an order of magnitude, highlighting a need for observational data o n large-scale abundance gradients in clusters. Our analysis indicates that the SNe energy input can be important for the heating of the entire ICM (pr oviding energy of similar to 1 keV per particle) only if the ICM abundances are uniform and the efficiency of the gas heating by SN explosions is clos e to 100 per cent (epsilon(SN) approximate to 1, implying that all of the i nitial kinetic energy of the explosion goes into heating of the ICM). The SNe energy input estimate made using simulations of galaxy formation is consistent with the above results derived from observed abundances, provid ed that large-scale radial abundance gradients exist in clusters. For the c luster AWM7, in which such a gradient has been observed, the energy input e stimated using observed metal abundances is similar to 0.01 and similar to 0.1 keV per particle for epsilon(SN) = 0.1 and epsilon(SN) = 1, respectivel y. These estimates fall far short of the required energy injection of simil ar to 0.5-3 keV per particle that appears to be needed to bring models of c luster formation into agreement with observations. Therefore our results in dicate that, unless the most favourable conditions are met, SNe alone are u nlikely to provide sufficient energy input and need to be supplemented or e ven substituted by some other heating process(es).