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Astron. Astrophys. 347, 1-20 (1999)

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The reheating and reionization history of the universe

Patrick Valageas 1,2 and Joseph Silk 2,3

1 Service de Physique Théorique, CEA Saclay, F-91191 Gif-sur-Yvette, France
2 Center for Particle Astrophysics, Department of Astronomy and Physics, University of California, Berkeley, CA 94720-7304, USA
3 Institut d'Astrophysique de Paris, CNRS, 98bis Boulevard Arago, F-75014 Paris, France

Received 22 September 1998 / Accepted 25 March 1999


We incorporate quasars into an analytic model to describe the reheating and reionization of the universe. In combination with a previous study of galaxies and Lyman-[FORMULA] clouds, we are able to provide a unified description of structure formation, verified against a large variety of observations. We also take into account the clumping of the baryonic gas in addition to the presence of collapsed objects.

We consider two cosmologies: a critical universe with a CDM power-spectrum and an open universe with [FORMULA], [FORMULA]. The derived quasar luminosity function agrees reasonably well with observations at [FORMULA] and with constraints over larger redshifts from the HDF. The radiation produced by these objects at [FORMULA] slowly reheats the universe which gets suddenly reionized at [FORMULA] for the open universe ([FORMULA] for the critical density universe). The UV background radiation simultaneously increases sharply to reach a maximum of [FORMULA] at [FORMULA], but shows strong ionization edges until [FORMULA]. The metallicity of the gas increases quickly at high z and is already larger than [FORMULA] at [FORMULA]. The QSO number counts and the helium opacity constrain the reionization redshift to be [FORMULA]. We confirm that a population of faint quasars is needed in order to satisfy the observations. Due to the low reionization redshift, the damping of CMB fluctuations is quite small, but future observations (e.g. with the NGST) of the multiplicity functions of radiation sources and of the HI and HeII opacities will strongly constrain scenarios in which reionization is due to QSOs. The reasonable agreement of our results with observations (for galaxies, quasars, Lyman-[FORMULA] clouds and reionization constraints) suggests that such a model should be fairly realistic.

Key words: cosmology: large-scale structure of Universe – galaxies: evolution – galaxies: quasars: general – galaxies: intergalactic medium

© European Southern Observatory (ESO) 1999

Online publication: June 18, 1999