用哈勃空间望远镜观测小麦哲伦云造父变星为 SH0ES 距离阶梯提供新锚点
Small Magellanic Cloud Cepheids Observed with the Hubble Space Telescope Provide a New Anchor for the SH0ES Distance Ladder
AI总结：
本研究利用 HST 对 SMC 核心 88 颗造父变星进行高精度测光，结合食双星几何距离作为新锚点，测得 H0=73.17±0.86 km/s/Mpc，并扩大金属丰度校准范围，揭示了与 ΛCDM 模型的 5.8σ 张力。
摘要：
我们展示了小麦哲伦云（SMC）核心区 88 颗造父变星的相位修正测光测量结果，这是利用哈勃空间望远镜（HST）的 Wide Field Camera 3 获得的首批样本，其测光系统与过去 SH0ES 距离阶梯上所有造父变星的测量保持相同的均匀体系。我们将样本限制在内核心区，并对几何结构进行建模，以减少先前研究中因该云非平凡深度导致的误差。由于没有地基研究中存在的拥挤效应，我们获得了 SMC 中前所未有的低色散周期-光度（P-L）关系，色散为 0.102 mag，接近造父变星不稳定带的宽度。SMC 中 15 个晚型相接食双星的新几何距离为改进距离阶梯的基础提供了难得机会，将校准星系数量从三个增加到四个。仅以 SMC 作为锚点，我们得到 H$_0\\!=\\!74.1 \pm 2.1$ km/s/Mpc。结合这四个几何距离与我们对 SMC 造父变星的 HST 测光数据，我们得到 H$_0\\!=\\!73.17 \pm 0.86$ km/s/Mpc。通过将 SMC 纳入距离阶梯，我们还将可校准造父变星 P-L 关系中金属丰度（[Fe/H]）依赖性的范围扩大了一倍，并得到 $γ= -0.234 \pm 0.052$ mag/dex。我们基于造父变星和 Ia 型超新星的 H$_0$ 局部测量值，与假设 Lambda 冷暗物质（$Λ$CDM）宇宙学从宇宙微波背景推断的值之间存在 5.8$σ$ 的张力，强化了存在超越 $Λ$CDM 物理的可能性。
英文摘要：
We present phase-corrected photometric measurements of 88 Cepheid variables in the core of the Small Magellanic Cloud (SMC), the first sample obtained with the Hubble Space Telescope's (HST) Wide Field Camera 3, in the same homogeneous photometric system as past measurements of all Cepheids on the SH0ES distance ladder. We limit the sample to the inner core and model the geometry to reduce errors in prior studies due to the nontrivial depth of this cloud. Without crowding present in ground-based studies, we obtain an unprecedentedly low dispersion of 0.102 mag for a period-luminosity (P-L) relation in the SMC, approaching the width of the Cepheid instability strip. The new geometric distance to 15 late-type detached eclipsing binaries in the SMC offers a rare opportunity to improve the foundation of the distance ladder, increasing the number of calibrating galaxies from three to four. With the SMC as the only anchor, we find H$_0\!=\!74.1 \pm 2.1$ km/s/Mpc. Combining these four geometric distances with our HST photometry of SMC Cepheids, we obtain H$_0\!=\!73.17 \pm 0.86$ km/s/Mpc. By including the SMC in the distance ladder, we also double the range where the metallicity ([Fe/H]) dependence of the Cepheid P-L relation can be calibrated, and we find $γ= -0.234 \pm 0.052$ mag/dex. Our local measurement of H$_0$ based on Cepheids and Type Ia supernovae shows a 5.8$σ$ tension with the value inferred from the cosmic microwave background assuming a Lambda cold dark matter ($Λ$CDM) cosmology, reinforcing the possibility of physics beyond $Λ$CDM.
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