Invited Review at the Xth Rencontres de Blois meeting "The Birth of Galaxies", eds. B. Guiderdoni (Gif-sur-Yvetter: Edition Frontieres). (astro-ph/9812087)


AFTER THE DARK AGES: THE EVOLUTION OF LUMINOUS SOURCES AT z < 5

Piero Madau

Space Telescope Science Institute, Baltimore, USA


ABSTRACT. I review recent observational and theoretical progress in our understanding of the cosmic evolution of luminous sources. Through a combination of deep HST 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 approx 1.5, a universal Salpeter IMF, and a moderate amount of dust with AV = 0.23 mag (A1500 = 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 approx 2 remains uncertain. If stellar sources are responsible for photoionizing the intergalactic medium at z approx 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 approx 3. A population of dusty AGNs at z ltapprox 2 could make a significant contribution to the FIR background if the accretion efficiency is ~ 10%.


Table of Contents

INTRODUCTION

EXTRAGALACTIC BACKGROUND LIGHT

STAR FORMATION HISTORY

THE STELLAR MASS DENSITY TODAY

A CONSTANT STAR-FORMATION DENSITY?

A POPULATION OF HIDDEN AGNS?

REIONIZATION OF THE IGM

REFERENCES

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