[论文解读] First Batch of Candidate Galaxies at Redshifts 11 to 20 Revealed by the James Webb Space Telescope Early Release Observations

Haojing Yan, Zhiyuan Ma+3 more|arXiv (Cornell University)|Jul 23, 2022

Astronomy and Astrophysical Research被引用 6

一句话总结

本文报告了利用詹姆斯·韦布空间望远镜（JWST）早期ERO数据，在SMACS 0723-73星系团场域中探测到87个红移z ≈ 11–20的高红移星系候选体。通过在六个NIRCam波段应用Lyman-break dropout技术，作者识别出红移后Lyman-break特征的天体，挑战了先前预测高红移星系数量急剧下降的模型，提示需要利用JWST进行光谱观测以确认其本质。

ABSTRACT

On July 13, 2022, NASA released to the whole world the data obtained by the James Webb Space Telescope (JWST) Early Release Observations (ERO). These are the first set of science-grade data from this long-awaited facility, marking the beginning of a new era in astronomy. In the study of the early universe, JWST will allow us to push far beyond z ~ 11, the redshift boundary previously imposed by the 1.7 um red cut-off of the Hubble Space Telescope (HST). In contrast, JWST's NIRCam reaches 5 um. Among the JWST ERO targets there is a nearby galaxy cluster SMACS 0723-73, which is a massive cluster and has been long recognized as a potential "cosmic telescope" in amplifying background galaxies. The ERO six-band NIRCam observations on this target have covered an additional flanking field not boosted by gravitational lensing, which also sees far beyond HST. Here we report the result from our search of candidate objects at z > 11 using these ERO data. In total, there are 87 such objects identified by using the standard "dropout" technique. These objects are all detected in multiple bands and therefore cannot be spurious. For most of them, their multi-band colors are inconsistent with known types of contaminants. If the detected dropout signature is interpreted as the expected Lyman-break, it implies that these objects are at z ~ 11--20. The large number of such candidate objects at such high redshifts is not expected from the previously favored predictions and demands further investigations. JWST spectroscopy on such objects will be critical.

研究动机与目标

• 利用詹姆斯·韦布空间望远镜（JWST）早期释放观测（ERO）的首批科学级数据，识别红移z > 11的高红移星系候选体。
• 检验观测到的高红移dropout特征是否与z ≈ 11–20星系预期的Lyman-break特征一致。
• 评估此类候选体的大量数量是否与现有理论预测的z ≈ 10以上星系数量密度急剧下降相矛盾。
• 通过确认其多波段检测并利用SED拟合排除常见污染源，评估候选体的稳健性。

提出的方法

• 应用标准的'dropout'技术，识别光谱能量分布（SED）在Lyman-break红移区出现凹陷的天体，表明其具有高红移特征。
• 利用SMACS 0723-73场的六波段NIRCam测光数据（F090W, F150W, F200W, F277W, F356W, F444W），识别在短波段缺失流量而长波段保留流量的天体。
• 使用Le Phare和EAZY-py代码结合恒星种群模型（BC03）进行SED拟合，估算测光红移并评估与高红移星系模板的一致性。
• 通过将观测颜色与已知污染源（如棕矮星、低红移星系）进行比较，评估dropout信号的显著性，并通过多波段检测确认以排除虚假源。
• 红移和星等计算采用宇宙学参数：ΩM = 0.27，ΩΛ = 0.73，H₀ = 71 km s⁻¹ Mpc⁻¹。
• 根据测光可靠性与模型一致性，按置信度等级（I–IV）对候选体进行分类。

实验结果

研究问题

• RQ1 JWST ERO数据在SMACS 0723-73场是否揭示了z ≈ 11–20星系候选体的统计显著性群体？
• RQ2 观测到的SED中dropout特征是否与高红移星系预期的Lyman-break一致，还是可由已知污染源解释？
• RQ3 z > 11候选体的数密度与现有早期星系形成宇宙学模型的预测相比如何？
• RQ4 这些候选体的测光红移估计的可靠性如何？不同SED拟合代码（Le Phare与EAZY）的结果如何比较？

主要发现

• 利用JWST ERO数据在SMACS 0723-73场中通过dropout技术共识别出87个红移z ≈ 11–20的高红移星系候选体。
• 所有候选体均在多个NIRCam波段被检测到，证实其真实性并排除了虚假检测。
• 大多数候选体的多波段颜色与已知污染源（如棕矮星或低红移星系）不一致。
• 观测到的z > 11候选体数密度超过先前模型的预测，而这些模型曾预测在z ≈ 10以上星系数量会急剧下降。
• 使用Le Phare和EAZY-py进行的SED拟合支持测光红移位于z ≈ 11–20范围内，最佳拟合模型显示出一致的Lyman-break特征。
• 结果表明，JWST光谱观测对于确认这些候选体的红移和物理特性至关重要，因为当前仅靠测光数据尚无法明确确定其本质。