A new determination of the primordial He abundance using the He i λ10830 Å emission line: cosmological implications

By Y. Izotov, T. Thuan, N. A. Observatory, Kyiv, Ukraine, U. Virginia, Charlottesville, Usa. 2014

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We present near-infrared spectroscopic observations of the high-intensity HeI 10830 emission line in 45 low-metallicity HII regions. We combined these NIR data with spectroscopic data in the optical range to derive the primordial He abundance. The use of the HeI 10830A line, the intensity of which is very sensitive to the density of the HII region, greatly improves the determination of the physical conditions in the He^+ zone. This results in a considerably tighter Y - O/H linear regression compared to all previous studies. We extracted a final sample of 28 HII regions with Hbeta equivalent width EW(Hbeta)>150A, excitation parameter O^2+/O>0.8, and with helium mass fraction Y derived with an accuracy better than 3%. With this final sample we derived a primordial He mass fraction Yp = 0.2551+/-0.0022. The derived value of Yp is higher than the one predicted by the standard big bang nucleosynthesis (SBBN) model. Using our derived Yp together with D/H = (2.53+/-0.04)x10^-5, and the chi^2 technique, we found that the best agreement between these light element abundances is achieved in a cosmological model with a baryon mass density Omega_b h^2 = 0.0240+/-0.0017 (68% CL), +/-0.0028 (95.4% CL), +/-0.0034 (99% CL) and an effective number of neutrino species Neff = 3.58+/-0.25 (68% CL), +/-0.40 (95.4% CL), +/-0.50 (99% CL). A non-standard value of Neff is preferred at the 99% CL, implying the possible existence of additional types of neutrino species.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/8e83a9264466f60527c477b3eeefd86ea430cc37

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Citations in the corpus

Precision big bang nucleosynthesis with improved Helium-4 predictions (2018, methodology): “After selecting 28 object, Izotov et al. (2014) obtained YP = 0.2551 ± 0.0022 for the 4He mass fraction.”
The trouble with H0 (2016, methodology): “The horizontal black dashed lines correspond to the measurement (mean and 1 and 2 σ) of the primordial abundance of [45], and in magenta of [46], both from chemical abundances in metal-poor HII regions.”
Elucidating ΛCDM: Impact of Baryon Acoustic Oscillation Measurements on the Hubble Constant Discrepancy (2017, result): “An important recent development is the use of the HeI line at 10830 Å to help break modeling degeneracies (Izotov et al. 2014).”
Stellar recipes for axion hunters (2017, background): “002 [104] – which propagates an additional uncertainty in R, σY = 0.”
The landscape of QCD axion models (2020, methodology): “(206), the analysis in [361] inferred an R parameter somewhat larger than observed, indicating a 2σ preference for a small, non-vanishing axion-photon coupling, later confirmed in [362] using an updated value of the He abundance [371, 372].”