On the supernova heating of the intergalactic medium

We present estimates of the energy input from supernovae (SNe) into the intergalactic medium using (i) recent measurements of Si and Fe abundances in the intracluster medium (ICM), and (ii) self-consistent gasdynamical simulations 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 uniformity of metal abundances in the ICM, and (ii) radial abundance gradients. We show that these two cases lead to energy input estimates which are different by an order of magnitude, highlighting a need for observational data on large-scale abundance gradients in clusters. Our analysis indicates that the SNe energy input can be important for the heating of the entire ICM (providing 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 close to 100 per cent (epsilon(SN) approximate to 1, implying that all of the initial 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, provided that large-scale radial abundance gradients exist in clusters. For the cluster AWM7, in which such a gradient has been observed, the energy input estimated 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, respectively. These estimates fall far short of the required energy injection of similar to 0.5-3 keV per particle that appears to be needed to bring models of cluster formation into agreement with observations. Therefore our results indicate that, unless the most favourable conditions are met, SNe alone are unlikely to provide sufficient energy input and need to be supplemented or even substituted by some other heating process(es).