Cosmological Reionization Caused by Structure Formation : Astrophysics and Relativity

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Various observations suggest that the universe is reionized at z<5 after the recombination at z〜 1000, but the epoch and mechanism of reionization of the universe is still an open issue. Recently, we proposed a qualitative scenario of cosmological reionization based on the structure formation and concluded that an early reionization of the universe at z>10 is possible if the power spectrum of the density fluctuations is sufficiently steep (Sasaki, Takahara and Suto, 1993). In this paper, we performed detailed numerical calculations based on the scenario and confirmed the results of the previous paper. In hierarchical clustering models of structure formation, numerous nonlinear objects on small scales would collapse much earlier than a redshift z〜10. Our scenario assumes that such objects dissipate their kinetic energy efficiently into heat and eventually provide copious ionizing photons which reionize the universe. We assume that the power spectrum of density fluctuation obeys a single power-law P(k)∝k^n on scales of interest at the standard recombination epoch. We find that in models with the spectral index n=-1 as long as the velocity dispersion at the present epoch is moderately large, the universe can be reionized at z≈5-20. For flatter spectra or lower efficiency, the universe remains effectively neutral. We also obtain the spectrum of background radiation at the present epoch. Furthermore, we compare our numerical results with various observations such as the Gunn-Peterson test, UV flux at z〜3 and the present intensity of background radiation at the optical, UV and soft X-ray bands.
理論物理学刊行会の論文
1994-04-25

Cosmological Reionization Caused by Structure Formation : Astrophysics and Relativity

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