Supernova Rates in Galaxy Clusters
  Measurements of SN rates in different environments and redshifts can shed light on the nature of SN-Ia progenitors, star formation history, and chemical enrichment history. I summarize some recent work by our group in this area, and discuss the implications. The current evidence favors production of most of the iron in the ICM (and perhaps everywhere) by core-collapse SNe, rather than SNe-Ia. These SNe may have been produced by the first, top-heavy-IMF, generation of stars that reionized the Universe. Improved rate measurements can sharpen the picture, and I describe our recent efforts in this direction. 
Dan Maoz