Supernovae and the intergalactic medium

An energetic argument implies that a galaxy like the Milky Way is blowing a powerful wind that carries away most of the heavy elements currently synthesized and has impacted the intergalactic medium (IGM) out to at least 180 kpc. Rich clusters of galaxies appear to be closed systems in which most heavy elements are ejected from galaxies. More supernovae (SNe) are required than the yield of core-collapse SNe from a Salpeter initial mass function. X-ray observations imply that the IGM in groups and clusters has been strongly preheated. SNe probably cannot supply the required energy, which must come from active galactic nuclei.