On the nature of the sources of the cosmic infrared background

We discuss the interpretation of the cosmic infrared background (CIB) anisotropies detected by us recently in the Spitzer/IRAC-based measurements. The fluctuations are approximately isotropic on the sky, which is consistent with their cosmological origin. They remain after the removal of fairly faint intervening sources and must arise from a population that has a strong CIB clustering component with only a small shot-noise level. We discuss the constraints the data place on the luminosities, epochs, and mass-to-light ratios of the individual sources producing them. Assuming the concordance Lambda CDM cosmology, the measurements imply that the luminous sources producing them lie at cosmic times <1 Gyr and were individually much brighter per unit mass than the present stellar populations.