[论文解读] Two multiple-imaged z=4.05 galaxies in the cluster-lens Abell 2390

R. Pelló, Jean‐Paul Kneib+9 more|arXiv (Cornell University)|Oct 23, 1998

Astronomy and Astrophysical Research被引用 5

一句话总结

本研究通过联合引力透镜建模、光谱红移测量与光谱验证，确认了在星系团透镜阿贝尔2390中存在两个红移z=4.05的极远距离、多重引力透镜化星系。这两个星系H3与H5表现出强烈的Ly-α发射线、高固有光度、团块状形态以及接近太阳金属度的特性，支持早期星系形成中预富集气体驱动高效局部恒星形成之层次并合情景。

ABSTRACT

We present the first results on the identification and study of very distant field galaxies in the core of cluster-lenses, using a selection criterium based on both lens modelling and photometric redshifts. We concentrate on two multiple-imaged sources at z=4.05 in the cluster A2390. The 2 objects presented in this paper, namely H3 and H5, were identified through lens modelling as multiple images of high-redshift sources at z>3.5. We confirm the excellent agreement between this identification and both their photometric redshifts and morphologies. Our CFHT/WHT program for a systematic redshift survey of arcs in clusters has allowed to obtain a set of spectra on 3 different images at z~4: the brightest image of H3, which redshift was already confirmed by Frye & Broadhurst (1998), and the two brightest images of H5. The later is then confirmed spectroscopically as a multiple image, giving a strong support to the lens model. The main feature in each of these spectra is a strong emission line, identified as Ly-alpha, leading to z=4.05 for both H3 and H5. The spectrophotometric properties of these galaxies are studied, in particular the degeneracy in the parameter-space defined by the SFR type, age, metallicity and reddening. H3 and H5 are intrinsically bright and clumpy sources located ~100 kpc part on the source plane, with mean metallicities compatible with a fraction of solar or even solar values. All these results seem to favour a hierarchical merging scenario, where we are actually seeing a relatively advanced step for these 2 z~4 objects, with stars forming locally and efficiently from a preenriched gas.

研究动机与目标

• 通过结合引力透镜建模与光谱红移方法，识别并确认阿贝尔2390星系团核心的高红移星系。
• 通过光谱学确认遥远星系的多重像，以验证透镜模型。
• 表征这些高红移源的光谱测光特性，包括恒星形成率、年龄、金属度与尘埃消光。
• 评估这些星系的观测特性是否支持早期星系形成中的层次并合情景。
• 通过研究强引力透镜场中本征明亮、团块状的星系，增进对z~4时星系演化的理解。

提出的方法

• 利用引力透镜建模预测阿贝尔2390星系团核心高红移源的多重像。
• 应用光谱红移技术，基于宽波段测光识别候选高红移星系。
• 使用CFHT与WHT望远镜对两个源（H3与H5）的三重像开展光谱调查。
• 在光谱中识别出Ly-α发射线，确认H3与H5的红移均为z=4.05。
• 通过涵盖恒星形成率类型、年龄、金属度与尘埃消光的参数空间分析光谱测光特性。
• 将形态与测光数据与透镜模型预测进行比较，以验证像的多重性与源平面位置。

实验结果

研究问题

• RQ1 阿贝尔2390星系团核心的多重像是否与红移z>3.5的高红移星系一致？
• RQ2 Ly-α发射线的光谱确认能否验证透镜模型与像的关联？
• RQ3 这些z=4.05星系的本征光谱测光特性（SFR、年龄、金属度、消光）为何？
• RQ4 这些星系的观测特性是否支持早期星系形成中的层次并合情景？
• RQ5 这些高红移星系的形态与金属度与标准形成模型的预期相比如何？

主要发现

• 通过光谱学确认了两个红移z=4.05的多重像星系H3与H5，其红移由强烈的Ly-α发射线确定。
• H5多重像的光谱确认强有力支持了透镜模型，验证了建模方法的可靠性。
• H3与H5为本征明亮、团块状星系，其在源平面上相距约100 kpc。
• 星系的平均金属度与太阳金属度或接近太阳金属度相兼容，表明其星际介质已预先富集。
• 光谱测光分析显示，恒星形成率类型、年龄、金属度与尘埃消光在参数空间中存在退化，但更支持高效、局部的恒星形成。
• 观测特性强烈支持一种层次并合情景：在z~4时，预富集气体在演化较成熟的阶段高效形成恒星。