[论文解读] Bursty Star Formation Naturally Explains the Abundance of Bright Galaxies at Cosmic Dawn

Guochao Sun, Claude‐André Faucher‐Giguère+4 more|arXiv (Cornell University)|Jul 28, 2023

Galaxies: Formation, Evolution, Phenomena被引用 5

一句话总结

本研究表明，在宇宙学模拟中，爆发式恒星形成可自然重现宇宙黎明时期（z ≳ 10）观测到的明亮星系丰度，而无需引入非标准物理。利用标准恒星反馈的FIRE-2聚焦模拟，作者表明，时间可变的恒星形成历史可使紫外明亮星系数量增加数个数量级，与詹姆斯·韦伯太空望远镜（JWST）观测结果一致，且无需微调参数，也无需引入顶重初始质量函数（IMF）、增强的恒星形成效率（SFE）或修改的宇宙学参数。

ABSTRACT

Recent discoveries of a significant population of bright galaxies at cosmic dawn $\left(z \gtrsim 10 ight)$ have enabled critical tests of cosmological galaxy formation models. In particular, the bright end of the galaxy UV luminosity function (UVLF) appears higher than predicted by many models. Using approximately 25,000 galaxy snapshots at $8 \leq z \leq 12$ in a suite of FIRE-2 cosmological "zoom-in'' simulations from the Feedback in Realistic Environments (FIRE) project, we show that the observed abundance of UV-bright galaxies at cosmic dawn is reproduced in these simulations with a multi-channel implementation of standard stellar feedback processes, without any fine-tuning. Notably, we find no need to invoke previously suggested modifications such as a non-standard cosmology, a top-heavy stellar initial mass function, or a strongly enhanced star formation efficiency. We contrast the UVLFs predicted by bursty star formation in these original simulations to those derived from star formation histories (SFHs) smoothed over prescribed timescales (e.g., 100 Myr). The comparison demonstrates that the strongly time-variable SFHs predicted by the FIRE simulations play a key role in correctly reproducing the observed, bright-end UVLFs at cosmic dawn: the bursty SFHs induce order-or-magnitude changes in the abundance of UV-bright ($M_\mathrm{UV} \lesssim -20$) galaxies at $z \gtrsim 10$. The predicted bright-end UVLFs are consistent with both the spectroscopically confirmed population and the photometrically selected candidates. We also find good agreement between the predicted and observationally inferred integrated UV luminosity densities, which evolve more weakly with redshift in FIRE than suggested by some other models.

研究动机与目标

• 解决标准星系形成模型预测与观测到的z ≳ 10时紫外明亮星系高丰度之间的矛盾。
• 检验爆发式恒星形成（无需微调）是否能重现观测到的明亮端紫外光度函数（UVLF）。
• 评估以往解释（如顶重初始质量函数、增强的恒星形成效率或非标准宇宙学）是否必要。
• 比较模拟中时间可变恒星形成历史与平滑恒星形成历史（SFH）的UVLF差异。
• 评估预测的紫外光度密度与光谱确认及光度选星系的观测约束的一致性。

提出的方法

• 利用26个FIRE-2宇宙学聚焦模拟中约25,000个星系快照，覆盖红移z = 8至12。
• 使用BPASS恒星群体合成代码计算每个快照中星系的紫外星等（M_UV）。
• 通过按红移和星等分箱构建UVLF，采用10–20 Myr的时间采样率以捕捉时间可变的恒星形成率（SFR）。
• 将原始爆发式SFH的UVLF与人工平滑SFH（如100 Myr timescale）的UVLF进行比较，以分离爆发性的作用。
• 使用GizmoAnalysis和hmf软件进行晕和星系属性分析及晕质量函数计算。
• 通过随机排除一半快照验证结果，确认统计采样的稳健性。

Figure 1: Top: UV magnitude–halo mass relations at $z=8$ –12. Data for individual galaxies are denoted by the grey dots (no smoothing applied to the SFH). The thick solid curves indicate the range of the 5th and 95th percentiles in the “bursty” and “smoothed” cases, from which the suppression of bri

实验结果

研究问题

• RQ1 在宇宙学模拟中，标准恒星反馈是否能重现z ≳ 10时观测到的紫外明亮星系丰度？
• RQ2 爆发式恒星形成历史在多大程度上提升了宇宙黎明时期M_UV ≲ -20星系的数量？
• RQ3 观测到的明亮端UVLF是否与使用标准物理且无微调参数的模拟预测一致？
• RQ4 与100 Myr timescale的平滑SFH相比，爆发式SFH的UVLF有何差异？
• RQ5 预测的紫外光度密度是否与光谱确认和光度选星系的观测估计一致？

主要发现

• 在FIRE-2模拟中，仅使用标准恒星反馈且无需微调，即可自然重现z ≳ 10时紫外明亮星系（M_UV ≲ -20）的观测丰度。
• 与平滑SFH相比，爆发式恒星形成历史使紫外明亮星系数量增加一个数量级，从而解释了高明亮端UVLF。
• 预测的UVLF与z ≳ 10时光谱确认星系及光度选候选星系的观测结果一致。
• 预测的总紫外光度密度随红移的演化比许多先前模型更弱，与观测约束一致。
• 无需引入顶重初始质量函数、增强的恒星形成效率或非标准宇宙学来解释观测结果。
• 通过随机子采样验证了UVLF测量的统计稳健性，表明快照采样率未引入偏差。

Figure 2: Dust-free UVLFs at $z=8$ , 10, and 12 predicted by the FIRE-2 simulations and from the literature. The binned and the best-fit, double-power law UVLFs are denoted by the crosses and solid curves, as specified in Table 1 and Equation ( 1 ), respectively. Several example dust-free prediction