Faint galaxies, extragalactic background light, and the reionization of the Universe

Details Faint galaxies, extragalactic background light, and the reionization of the Universe Faint galaxies, extragalactic background light, and the reionization of the Universe

1999-01-18

arxiv.org/abs/astro-ph/9901237v1

Astronomy and Astrophysics

Astrophysics

LateX, 13 pages, aipproc.sty, 5 figures. To appear in the proceedings of the 9th Annual October Astrophysics Conference in Mar

Scientific paper

10.1063/1.58615

I review recent observational and theoretical progress in our understanding of the cosmic evolution of luminous sources. Largely due to a combination of deep HST imaging, Keck spectroscopy, and COBE far-IR background measurements, new constraints have emerged on the emission history of the galaxy population as a whole. Barring large systematic effects, the global ultraviolet, optical, near- and far-IR photometric properties of galaxies as a function of cosmic time cannot be reproduced by a simple stellar evolution model defined by a constant (comoving) star-formation density and a universal (Salpeter) IMF, and require instead a substantial increase in the stellar birthrate with lookback time. While the bulk of the stars present today appears to have formed relatively recently, the existence of a decline in the star-formation density above z=2 remains uncertain. The history of the transition from the cosmic `dark age' to a ionized universe populated with luminous sources can constrain the star formation activity at high redshifts. 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, Type II AGNs at z<2 could make a significant contribution to the FIR background if the accretion efficiency is of order 10%.

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