Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 467, Issue 4, Pages 4050-4056Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stx306
Keywords
cosmic background radiation
Categories
Funding
- National Science Foundation [PHY-1066293]
- NASA ATP [NNX15AK22G]
- US Dept. of Energy [DEFG02-13ER41958]
- Kavli Institute for Cosmological Physics at the University of Chicago [NSF PHY-0114422, NSF PHY-0551142]
- Charles E. Kaufman Foundation
- Pittsburgh Foundation
- National Science Foundation [PHY-1066293]
- NASA ATP [NNX15AK22G]
- US Dept. of Energy [DEFG02-13ER41958]
- Kavli Institute for Cosmological Physics at the University of Chicago [NSF PHY-0114422, NSF PHY-0551142]
- Charles E. Kaufman Foundation
- Pittsburgh Foundation
- Division Of Physics
- Direct For Mathematical & Physical Scien [1125897] Funding Source: National Science Foundation
- NASA [806105, NNX15AK22G] Funding Source: Federal RePORTER
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Standard analyses of the reionization history of the Universe from Planck cosmic microwave background (CMB) polarization measurements consider only the overall optical depth to electron scattering (t), and further assume a step-like reionization history. However, the polarization data contain information beyond the overall optical depth, and the assumption of a step-like function may miss high redshift contributions to the optical depth and leads to biased t constraints. Accounting for its full reionization information content, we reconsider the interpretation of Planck 2015 Low-Frequency Instrument (LFI) polarization data using simple, yet physically motivated reionization models. We show that these measurements still, in fact, allow a non-negligible contribution from metal-free (Pop-III) stars forming in mini-haloes of mass M similar to 10(5)-10(6) M-circle dot at z greater than or similar to 15, provided this mode of star formation is fairly inefficient. We find that an early, self-regulated phase of Pop-III star formation with a gradual, plateau feature in the ionization history provides a good match to the Planck LFI measurements. In this case, as much as 20 per cent of the volume of the Universe is ionized by z similar to 20. Although preferred when the full information content of the data is incorporated, this model would spuriously be disfavoured in the standard analysis. This preference is driven mostly by excess power from E-mode polarization at multipoles of 10 less than or similar to l less than or similar to 20, which may reflect remaining systematic errors in the data, a statistical fluctuation or signatures of the first stars. Measurements from the Planck High-Frequency Instrument should be able to confirm or refute this hint and future cosmic-variance- limited E-mode polarization surveys can provide substantially more information on these signatures.
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