Cosmic Microwave Background Constraints in Light of Priors Over Reionization Histories

Abstract

Non-parametric reconstruction or marginalization over the history of reionization using cosmic microwave background data necessarily assumes a prior over possible histories. We show that different but reasonable choices of priors can shift current and future constraints on the reionization optical depth, $\tau$, or correlated parameters such as the neutrino mass sum, $\Sigma m_{\nu }$, at the level of 0.3-0.4$\sigma$, i.e., that this analysis is somewhat prior dependent. We point out some prior-related problems with the commonly used principal component reconstruction, concluding that the significance of some recent hints of early reionization in Planck 2015 data has been overestimated. We also present the first non-parametric reconstruction applied to newer Planck intermediate (2016) data and find that the hints of early reionization disappear entirely in this more precise dataset. These results limit possible explanations of the EDGES 21cm signal which would have also significantly reionized the universe at $z>15$. Our findings about the dependence on priors motivate the pursuit of improved data or searches for physical reionization models which can reduce the prior volume. The discussion here of priors is of general applicability to other non-parametric reconstructions, for example of the primordial power spectrum, of the recombination history, or of the expansion rate.

13 pages, 7 figures, submitted to Astronomy & Astrophysics

References in corpus (11)

• Astrophysics Source Code Library
• An absorption profile centred at 78 megahertz in the sky-averaged spectrum
• PolyChord: nested sampling for cosmology
• Model selection applied to reconstruction of the Primordial Power Spectrum
• The Cosmic Microwave Background and the Ionization History of the Universe
• Reionization constraints from five-year WMAP data
• Witnessing the reionization history using Cosmic Microwave Background observation from Planck
• Beyond CMB cosmic variance limits on reionization with the polarized SZ effect
• Inflationary vs. Reionization Features from Planck 2015 Data
• Model independent approaches to reionization in the analysis of upcoming CMB data
• Was there an early reionization component in our universe?

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• Retrieving cosmological information from small-scale CMB foregrounds II. The kinetic Sunyaev Zel'dovich effect
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