Primordial He abundance from extremely metal-poor galaxies: Implications for the lepton asymmetry and the H0 tension


2022/05/19 12:30 – 13:30


Online (Zoom)


Akinori Matsumoto (The University of Tokyo)





Motoo Suzuki /


The primordial He abundance is best determined by observations of metal-poor galaxies, while there are only a few known extremely metal-poor (< 0.1Z⊙) galaxies (EMPGs) having reliable He/H measurements. We present deep Subaru NIR spectroscopy for 10 EMPGs and determination of the He/H values with NIR HeI10830A line and optical emission lines. Adding pre-existing galaxies with reliable He/H estimates to our sample, we obtain Yp = 0.2379+/-0.0030, which is slightly (∼ 1σ) smaller than the previous values. With the Yp constrain, the existing primordial deuterium Dp constraints, and a prior of baryon-to-photon ratio η, we obtain the degeneracy parameter of electron-neutrino ξe = 0.05+/-0.03, the effective number of neutrino species Neff = 3.22+/-0.3, and η×10^10 = 6.13+/-0.04 from the Yp and Dp measurements. Our constraints suggest a lepton asymmetry and allow for a high value of Neff up to Neff = 3.55 within the 1σ level, which could mitigate the Hubble tension.
This talk is based on the work presented in arXiv:2203.09617.