EMPRESS. VIII. A New Determination of Primordial He Abundance with Extremely Metal-poor Galaxies: A Suggestion of the Lepton Asymmetry and Implications for the Hubble Tension
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- Matsumoto_2022_ApJ_941_167
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The primordial He abundance Y P is a powerful probe of cosmology. Currently, Y P is best determined by observations of metal-poor galaxies, while there are only a few known local extremely metal-poor (<0.1Z ⊙) galaxies (EMPGs) having reliable He/H measurements with He i λ10830 near-infrared (NIR) emission. Here we present deep Subaru NIR spectroscopy for 10 EMPGs. Combining the existing optical data, He/H values of 5 out of the 10 EMPGs are reliably derived by the Markov chain Monte Carlo algorithm. Adding the existing 3 EMPGs and 51 moderately metal-poor (0.1-0.4Z ⊙) galaxies with reliable He/H estimates, we obtain Y P = 0.2370 − 0.0034 + 0.0033 by linear regression in the (He/H) − (O/H) plane, where we increase the number of EMPGs from three to eight anchoring He/H of the most metal-poor gas in galaxies. Although our Y P measurement and previous measurements are consistent, our result is slightly (∼1σ) smaller due to our EMPGs. Including the existing primordial deuterium D P measurement, we constrain the effective number of neutrino species N eff and the baryon-to-photon ratio η showing ≳1-2σ tensions with the Standard Model and Planck Collaboration et al. (2020). Motivated by the tensions, we allow the degeneracy parameter of the electron neutrino ξ e , as well as N eff and η, to vary. We obtain ξ e = 0.05 − 0.02 + 0.03 , N eff = 3.11 − 0.31 + 0.34 , and η × 10 10 = 6.08 − 0.06 + 0.06 from the Y P and D P measurements with a prior of η taken from Planck Collaboration et al. Our constraints suggest a lepton asymmetry and allow for a high value of N eff within the 1σ level, which could mitigate the Hubble tension.
Originalsprog | Engelsk |
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Artikelnummer | 167 |
Tidsskrift | Astrophysical Journal |
Vol/bind | 941 |
Udgave nummer | 2 |
Antal sider | 14 |
ISSN | 0004-637X |
DOI | |
Status | Udgivet - 1 dec. 2022 |
Bibliografisk note
Funding Information:
We thank the anonymous referee for a careful reading and valuable comments that improved the clarity of the paper. We are grateful to Erik Aver, Kazunori Kohri, Oleg Kurichin, and J. Xavier Prochaska for giving us helpful comments and discussions. This work is supported by the World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan, as well as KAKENHI Grant-in-Aid for Scientific Research (A)(20H00180, 21H04467, 21J00153, 20K14532, 21H04499, 21K03614, 21K03622, and 22H01259) through the Japan Society for the Promotion of Science (JSPS). This work was supported by the joint research program of the Institute for Cosmic Ray Research (ICRR), University of Tokyo.
Publisher Copyright:
© 2022. The Author(s). Published by the American Astronomical Society.
ID: 342931938