EMPRESS。VIII。一种新的用极贫金属镓确定原初氦原子的方法：轻子不对称性的建议和对哈勃张力的意义
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
摘要：
原始氦丰度$Y_\mathrm{P}$是宇宙学的有力探测器。目前，$Y_\mathrm{P}$最好是通过对贫金属星系的观测来确定，而只有少数已知的本地极端贫金属（$<0.1 Z_\odot$）星系（EMPGs）具有可靠的He/H测量与HeI $λ$ 10830近红外（NIR）发射。在这里，我们提出了深斯巴鲁近红外光谱的10个EMPG。结合已有的光学数据，用马尔可夫链蒙特卡罗算法可靠地计算了10个EMPG中5个的He/H值。将已有的3个EMPG和51个中等贫金属（$0.1-0.4 Z_\odot$）星系与可靠的He/H估计相加，在$\mathrm{(He/H)}-\mathrm{(O/H)}$平面上通过线性回归得到$Y_\mathrm{P}=0.2370^{+0.0034}_{-0.0033}$，其中我们将EMPG的数目从3个增加到8个，锚定星系中最贫金属气体的He/H。虽然我们的$Y_\mathrm{P}$测量和以前的测量是一致的，但由于我们的EMPG，我们的结果（$\sim 1σ$）略小。通过我们的$Y_\mathrm{P}$和现有的原始氘$D_\mathrm{P}$测量，我们限制了中微子物质$N_\mathrm{eff}$的有效数量和重子与光子的比率$η$，显示了标准模型和普朗克合作组织等人的$\gtrsim 1-2σ$张力。受张力的影响，我们允许电子中微子$ξ_e$的简并参数随$N_\mathrm{eff}$和$η$的变化而变化。我们从$Y_\mathrm{P}$和$D_\mathrm{P}$测量中获得$ξ_e = 0.05^{+0.03}_{-0.02}$、$N_\mathrm{eff}=3.11^{+0.34}_{-0.31}$和$η\times10^{10}=6.08^{+0.06}_{-0.06}$，其中$η$的先验值来自Planck Collaboration et al.（2020）。我们的限制表明轻子不对称性，并允许在$1σ$能级内有高的$N_\mathrm{eff}$值，这可以减轻哈勃张力。
英文摘要：
The primordial He abundance $Y_\mathrm{P}$ is a powerful probe of cosmology. Currently, $Y_\mathrm{P}$ is best determined by observations of metal-poor galaxies, while there are only a few known local extremely metal-poor ($<0.1 Z_\odot$) galaxies (EMPGs) having reliable He/H measurements with HeI$λ$10830 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 ($0.1-0.4 Z_\odot$) galaxies with reliable He/H estimates, we obtain $Y_\mathrm{P}=0.2370^{+0.0034}_{-0.0033}$ by linear regression in the $\mathrm{(He/H)}-\mathrm{(O/H)}$ plane, where we increase the number of EMPGs from 3 to 8 anchoring He/H of the most metal-poor gas in galaxies. Although our $Y_\mathrm{P}$ measurement and previous measurements are consistent, our result is slightly ($\sim 1σ$) smaller due to our EMPGs. With our $Y_\mathrm{P}$ and the existing primordial deuterium $D_\mathrm{P}$ measurement, we constrain the effective number of neutrino species $N_\mathrm{eff}$ and the baryon-to-photon ratio $η$ showing $\gtrsim 1-2σ$ tensions with the Standard Model and Planck Collaboration et al. (2020). Motivated by the tensions, we allow the degeneracy parameter of electron-neutrino $ξ_e$ to vary as well as $N_\mathrm{eff}$ and $η$. We obtain $ξ_e = 0.05^{+0.03}_{-0.02}$, $N_\mathrm{eff}=3.11^{+0.34}_{-0.31}$, and $η\times10^{10}=6.08^{+0.06}_{-0.06}$ from the $Y_\mathrm{P}$ and $D_\mathrm{P}$ measurements with a prior of $η$ taken from Planck Collaboration et al. (2020). Our constraints suggest a lepton asymmetry and allow for a high value of $N_\mathrm{eff}$ within the $1σ$ level, which could mitigate the Hubble tension.
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