Setting the stage: Ultralumnous galaxies in a cosmological context

I will try to put the ultraluminous galaxy phenomenon into a broad cosmological context. Viewed from this perspective, the significance of ultraluminous galaxies and the `starburst vs. monster' debate becomes clear. Ultraluminous galaxies are fascinating in their own right, allow detailed study of the processes by which massive spheroids were built and the IGM was heated and polluted, and resemble the most luminous and dustiest galaxies at high-redshift. Ultraluminous galaxies were apparently far more common at z similar to 3 than today. Recent inventories in the local universe of the cumulative effect of nuclear burning (metal production) and of monster-feeding (compact dark objects in galactic nuclei) imply that either stars or monsters could have generated the observed far-IR cosmic background. The starburst vs. monster debate has global, as well as local importance.