After the Dark Ages: the Evolution of Luminous Sources at z<5

Abstract

I review recent observational and theoretical progress in our understanding of the cosmic evolution of luminous sources. Through a combination of deep imaging, Keck spectroscopy, and COBE background measurements, important constraints have emerged on the emission history of the galaxy population as a whole. A simple stellar evolution model, defined by a star-formation density that rises from z=0 to z=1.5, a universal Salpeter IMF, and a moderate amount of dust with A_V=0.23 mag (A_1500=1.2 mag), is able to account for most of the optical-FIR extragalactic background light, and reproduces the global ultraviolet, optical, and near-IR photometric properties of the universe. By contrast, a star-formation density that stayed roughly constant at all epochs appears to overproduce the local K-band luminosity density. While the bulk of the stars present today formed relatively recently, the existence of a decline in the star-formation density above z=2 remains uncertain. If stellar sources are responsible for photoionizing the intergalactic medium at z=5, the rate of star formation at this epoch must be comparable or greater than the one inferred from optical observations of galaxies at z=3. A population of dusty AGNs at z>2 could make a significant contribution to the FIR background if the accretion efficiency is close to 10%.