Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 451, Issue 2, Pages 1875-1882Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stv1064
Keywords
intergalactic medium; quasars: general; dark ages, reionization, first stars
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Funding
- National Basic Research Program of China [2012CB821801]
- Chinese Academy of Sciences [XDB09000000]
- National Natural Science Foundation [U1431228, 11133005, 11233003, 11421303, 11333008, 11233005, 11273061]
- 973 program [2015CB857000, 2013CB834900]
- foundation for Distinguished Young Scholars of Jiangsu Province [BK20140050]
- CAS [XDB09010000]
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Observations on the high-redshift galaxies at z > 6 imply that their ionizing emissivity is unable to fully reionize the Universe at z similar to 6. Either a high escape fraction of ionizing photons from these galaxies or a large population of faint galaxies below the detection limit is required. However, these requirements are somewhat in tension with present observations. In this work, we explored the combined contribution of mini-quasars and stars to the reionization of cosmic hydrogen and helium. Our model is roughly consistent with (1) the low escape fractions of ionizing photons from the observed galaxies, (2) the optical depth of cosmic microwave background measured by the 7-yr Wilkinson Microwave Anisotropy Probe and (3) the redshift of the end of hydrogen and helium reionization at z approximate to 6 and z approximate to 3, respectively. Neither an extremely high escape fraction nor a large population of fainter galaxies is required in this scenario. In our most optimistic model, more than similar to 20 per cent of the cosmic helium is reionized by z similar to 6, and the ionized fraction of cosmic helium rapidly climbs to more than 50 per cent by z similar to 5. These results may imply that better measurements of helium reionization, especially at high redshifts, could be helpful in constraining the growth of intermediate-mass black holes in the early Universe, which would shed some light on the puzzles concerning the formation of supermassive black holes.
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