In the course of structure formation, only a small fraction of the baryons turned into stars - most remain in a diffuse intergalactic medium. The growth and evolution of galaxies is controlled by feedback processes, such as energy and momentum input from supernovae, and from the jets and winds of accreting supermassive black holes. I will start my talk by presenting observational results on the role of supermassive black holes in suppressing star formation in the most massive galaxies, keeping them 'red and dead'. Then, I will show how deep observations of extreme clusters of galaxies inform us about the microphysics of the intergalactic medium, which determines how the energy from accreting black holes couples with the diffuse gas. Then, I will 'zoom out' to the outskirts of galaxy clusters where we also find hints that supermassive black holes played an important role in the distant past. X-ray observations reveal a remarkably homogeneous distribution of iron out to the virial radius of the nearby Perseus Cluster, requiring that most of the metal enrichment of the intergalactic medium occurred before the cluster formed, probably more than ten billion years ago, during the period of maximal star formation and black hole activity. Finally, I will talk about the upcoming ASTRO-H satellite which will revolutionize X-ray spectroscopy and our understanding of the physics of galactic feedback.
