1998/04/27 by Piero Madau, Madau, Piero
Physics and Astronomy · #Advanced Mathematical Theories and Applications #Astrophysics (astro-ph) #Cosmology and Gravitation Theories #FOS: Physical sciences #Relativity and Gravitational Theory #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9804280
LaTeX, 9 pages, 2 postscript figures, to appear in "Molecular Hydrogen in the Early Universe", eds. E. Corbelli, D. Galli, & F. Palla, Mem. S.A.It., in press (1998)
arxiv created 1998/04/27 · openalex publication_date 1998/04/27 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The history of the transition from a neutral intergalactic medium to one that is almost fully ionized can reveal the character of cosmological ionizing sources. In this talk I will discuss the implications for rival reionization scenarios of the rapid decline observed in the space density of quasars and star-forming galaxies at redshifts z>3. The hydrogen component in a highly inhomogeneous universe is completely reionized when the number of ionizing photons emitted in one recombination time equals the mean number of hydrogen atoms. At z=5, the local character of the UV metagalactic flux allows one to define a critical emission rate of hydrogen-ionizing photons per unit comoving volume. Models based on photoionization by bright QSOs and/or young galaxies with star formation rates in excess of 0.3-1 Msun/yr appear to fail to provide the required number of hydrogen-ionizing photons at these redshifts by large factors. If stellar sources are responsible for keeping the universe ionized at z=5, the rate of star formation per unit comoving volume at this epoch must be comparable or greater than observed at z=3.