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components, which can be measured in potential wells from the richest clusters to the poorest galaxies. For the richest clusters of galaxies, most of the baryons are accounted for in that the baryon fraction approaches the cosmological value, within theoretical expectations. Progressing toward shallower potential wells, the baryon fraction decreases slowly until temperatures of about 1E6 K, below which the baryon fraction decreases quickly. This trend of decreasing baryon content continues through galaxies, where the Milky Way is missing about 75% of its baryons and the typical (lower mass) galaxy is missing 90% of <br>
its baryons. The missing baryons do not surround the galaxies as hot halos and we argue that the material never fell into these galaxies, having been pre-heated by an early population of supernovae. Furthermore, we show that the heating and metallicity contributions from this early population of stars may be largely independent of galaxies as well.