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[论文解读] Bound star clusters observed in a lensed galaxy 460 Myr after the Big Bang

Angela Adamo, Larry Bradley|arXiv (Cornell University)|Jan 6, 2024
Galaxies: Formation, Evolution, Phenomena被引用 6
一句话总结

该论文报道在强引力透镜放大的星系 SPT0615-JD1（Cosmic Gems 弧）中发现五个有边界的巨大星团，红移 z~10.2，对应大爆炸后约460 Myr，尺寸约 ~1 pc，恒星密度高，且可能是原恒星球团的前身。

ABSTRACT

The Cosmic Gems arc is among the brightest and highly magnified galaxies observed at redshift $z\sim10.2$. However, it is an intrinsically UV faint galaxy, in the range of those now thought to drive the reionization of the Universe. Hitherto the smallest features resolved in a galaxy at a comparable redshift are between a few hundreds and a few tens of parsecs. Here we report JWST observations of the Cosmic Gems. The light of the galaxy is resolved into five star clusters located in a region smaller than 70 parsec. They exhibit minimal dust attenuation and low metallicity, ages younger than 50 Myr and intrinsic masses of $\sim10^6$ M$_{\odot}$. Their lensing-corrected sizes are approximately 1 pc, resulting in stellar surface densities near $10^5$~M$_{\odot}$/pc$^2$, three orders of magnitude higher than typical young star clusters in the local universe. Despite the uncertainties inherent to the lensing model, they are consistent with being gravitationally bound stellar systems, i.e., proto-globular clusters. We conclude that star cluster formation and feedback likely contributed to shape the properties of galaxies during the epoch of reionization. [Abridged]

研究动机与目标

  • 研究被强引力透镜放大的再电离时代星系的恒星内容。
  • 在 Cosmic Gems 弧中识别并表征紧凑星团。
  • 评估这些星团是否受引力束缚，以及是否可能成为原生球状星团的候选。

提出的方法

  • 对 SPT-CL J0615−5746 领域的 Cosmic Gems 弧，在 8 个波段（0.8–5 μm）使用 JWST/NIRCam 成像。
  • 通过对 F150W 数据拟合二维高斯光分布并去卷积点扩散函数来建模星团尺寸和通量。
  • 利用 Lenstool-A 和独立前向建模（源平面重建）推导校正透镜效应的物理性质，以估计尺寸和放大率。
  • 使用 BAGPIPES 进行 SED 拟合，采用多种 SFH 假设（τ=1 Myr 的指数衰减、单次爆发，以及基于 BPASS 的模板），固定在 z=10.2。
  • 通过穿越时间估算动力学年龄以评估引力束缚（Pi = Age / t_cross）。
  • 将观测性质与其他透镜化高红移星团及局部球状星团对应物进行比较。
Figure 1: Top left: JWST color image of the $z_{\rm phot}\sim 10.2$ Cosmic Gems arc observed in rest-frame ultraviolet, blue optical wavelengths (1200–2800 Å). The 5 ′′ arrow shows the full extent of the arc down to the faintest emission. A foreground galaxy at redshift $z_{\rm phot}=2.6$ is visible
Figure 1: Top left: JWST color image of the $z_{\rm phot}\sim 10.2$ Cosmic Gems arc observed in rest-frame ultraviolet, blue optical wavelengths (1200–2800 Å). The 5 ′′ arrow shows the full extent of the arc down to the faintest emission. A foreground galaxy at redshift $z_{\rm phot}=2.6$ is visible

实验结果

研究问题

  • RQ1Cosmic Gems 弧中星团的尺寸、质量和年龄是多少？
  • RQ2这些星团是否受引力束缚，能够演变为球状星团吗？
  • RQ3宿主星系的紫外光有多少来自星团，这对 z~10 时的星团形成效率有何启示？
  • RQ4这些星团的特性与其他透镜化星系中的星团以及局部星团相比如何？

主要发现

  • 在 Img.1 中辨识出五个星团候选体，透镜效应校正后的半径 ~1 pc。
  • 每个星团的固有质量约为 ~0.7–3×10^6 M⊙，总星团质量约为 7.2×10^6 M⊙，贡献约 60% 的宿主 F150W 通量。
  • 恒星表面密度约为 ~10^5 M⊙/pc^2，远高于典型局部年轻星团，高出约三个数量级。
  • 动力学年龄（Pi）显著大于1，表明有界星团；可能成为真正的 proto-globular clusters，在 Big Bang 之后不到 500 Myr 形成。
  • 该星系的星形成主要以簇化模式进行，在某些 CMF 假设下，簇形成效率 (CFE) 的下限 ≥30%，上限约 85%。
  • 星团极其紧凑，且靠近透镜临界曲线，使得在 z~10 时达到点到 pc 级的分辨率成为可能。
Figure 2: Star cluster stellar surface density versus half-light radius R eff . The star clusters in the $z_{\rm phot}\sim 10.2$ Cosmic Gems arc are shown color-coded by their dynamical age ( $\log(\Pi)$ ). The plotted values have been derived using the reference lensing model. Predictions by other
Figure 2: Star cluster stellar surface density versus half-light radius R eff . The star clusters in the $z_{\rm phot}\sim 10.2$ Cosmic Gems arc are shown color-coded by their dynamical age ( $\log(\Pi)$ ). The plotted values have been derived using the reference lensing model. Predictions by other

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