A Realistic Determination of the Error on the Primordial Helium Abundance: Steps toward Nonparametric Nebular Helium Abundances

By K. Olive, E. Skillman. 2004

185 citations recorded by the source corpus.

Using the WMAP determination of the baryon density, the standard model of big bang nucleosynthesis yields relatively precise predictions of the primordial light-element abundances. Currently there are two significantly different observational determinations of the primordial helium abundance, and if only statistical errors in 4He abundance determinations are considered, the discrepancies between the observational determinations and the value favored by the WMAP results are significant. Here we examine in detail some likely sources of systematic uncertainties that may resolve the differences between the two determinations. We conclude that the observational determination of the primordial helium abundance is completely limited by systematic errors and that these systematic errors have not been fully accounted for in any published observational determination of the primordial helium abundance. In principle, the observed metal-poor H II region spectra should be analyzed in a nonparametric way, such that the H II region physical conditions and the helium abundance are derived solely from the relative flux ratios of the helium and hydrogen emission lines. In practice, there are very few H II region spectra with the quality that allows this, so that most analyses depend on assumed ranges or relationships between physical parameters, resulting in parametric solutions with underestimated error bars. A representative result of our analysis yields Yp = 0.249 ± 0.009. We stress that the main result of the present work is the increase in the size of the uncertainty rather than the shift in the primordial value. Furthermore, given that most of the spectra analyzed to date do not significantly constrain the primordial helium abundance, we argue in favor of a range of allowed values of 0.232 ≤ Yp ≤ 0.258. This easily allows for concordance between measurements of the baryon-to-photon ratio (η) from WMAP, deuterium abundances, and helium abundance (although the discrepancy with lithium remains).

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/7070b5c10e2222d202a46675a0224e33cd599f8b

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Citations in the corpus

SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP) OBSERVATIONS: COSMOLOGICAL INTERPRETATION (2010, result): “This value is broadly consistent with the helium abundances estimated from observations of low-metallicity extragalactic ionized (HII) regions, Yp ≃ 0.24 − 0.25 (Gruenwald et al. 2002; Izotov & Thuan 2004; Olive & Skillman 2004; Fukugita & Kawasaki 2006; Peimbert et al. 2007).”
Varying Constants, Gravitation and Cosmology (2010, background): “ and got a bound on the variation of the radius of the extra-dimensions. Although the uncertainty in the helium-4 abundance has been argued to be signiﬁcantly larger that what was assumed in the past [394], interesting bounds can still be derived [116]. In particular translating the bound on extra r”
Revised Primordial Helium Abundance Based on New Atomic Data (2007, background): “It has been argued that the uncertainty on Yp is dominated by systematic errors (Olive & Skillman 2004).”
Detection of extended He II reionization in the temperature evolution of the intergalactic medium (2010, background): “The IGM is assumed to be of primordial composition with a helium fraction by mass of Y = 0.24 (Olive & Skillman 2004).”
SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP) OBSERVATIONS: POWER SPECTRA AND WMAP-DERIVED PARAMETERS (2010, background): “…as a function of metallicity can be observed and the relation can be regressed to zero metallicity, which is presumed to give the primordial abundance (Gruenwald et al. 2002; Izotov & Thuan 2004; Olive & Skillman 2004; Fukugita & Kawasaki 2006; Peimbert et al. 2007) as reviewed by Steigman (2007).”
The Primordial Abundance of 4He: A Self-consistent Empirical Analysis of Systematic Effects in a Large Sample of Low-Metallicity H II Regions (2007, methodology): “Our Yp range is much smaller than the one of 0.009 claimed by Olive & Skillman (2004).”
A new approach to systematic uncertainties and self-consistency in helium abundance determinations (2010, methodology): “The spectrum for Mrk 193 originally reported in Izotov, Thuan, & Lipovetsky (1994) and used in Olive & Skillman (2004) has been reanalyzed and the results of the new analyses are reported in Izotov et al. (2007).”