The primordial helium abundance: No problem

We have used Markov Chain Monte Carlo (MCMC) techniques to analyze the large dataset of Izotov, Thuan, and Stasinska. We draw attention to the use of χ² as a clear measure of the quality of the physical solution for individual spectra and adopt this measure in order to cut the sample to reliable solutions. We also emphasize the importance of the He I λ4026 emission line for its sensitivity to underlying absorption. The final dataset, after cuts, exhibits improved consistency. Regression to zero metallicity yields Y_p = 0.2534 ± 0.0083, in agreement with the WMAP result of 0.2487 ± 0.0002. Using the same dataset, Izotov and Thuan have argued that their derived value of the primordial helium abundance (Y_p) is inconsistent with the value derived from WMAP assuming standard big bang nucleosynthesis, in the sense that their determination is too high by two sigma. Our result indicates that it is premature to emphasize a discrepancy.