[论文解读] The Discovery of Primeval Galaxies and the Epoch of Galaxy Formation

Max Pettini, Charles C. Steidel+4 more|arXiv (Cornell University)|Aug 12, 1997

Astronomy and Astrophysical Research被引用 4

一句话总结

本文提出了一种基于912 Å处莱曼间断的测光选择技术，用于在红移z ≈ 3处发现原初星系，揭示了一类具有强烈星风和中等尘埃消光的明亮、星形成活跃的星系。该方法证实了大尺度结构的早期形成，表明暗物质晕质量超过10¹² M☉，并强调了未来红外空间望远镜在探测z > 5星系中的必要性。

ABSTRACT

We review the steps which have led to the discovery of a widespread population of objects at z = 3 with many of the characteristics which we expect for primeval galaxies, and emphasize in particular the advantages of a colour selection technique which targets the Lyman discontinuity at 912 Angstroms. Star forming galaxies at z = 3 resemble local starbursts, although they are typically more luminous by more than one order of magnitude. The ultraviolet continuum is dominated by the integrated light of O and early B type stars and shows prominent interstellar absorption lines which are often blueshifted relative to the systemic velocity of the galaxy, indicating highly energetic outflows in the interstellar medium. Lyman alpha emission is generally weak, probably as a result of resonant scattering. The spectral slope of the ultraviolet continuum and the strength of the Hbeta emission line, which we have detected in a few cases with pilot observations in the infrared K band, suggest that some interstellar dust is already present in these young galaxies and that it attenuates their UV luminosities by a factor of about 3. The efficiency of our photometric selection technique has allowed us to establish that large scale concentrations of galaxies were already in place at z = 3, possibly the precursors of galaxy clusters as they as they were beginning to decouple from the Hubble expansion. In the context of Cold Dark Matter models of structure formation, the observed clustering of the z~3 galaxies suggests that they are associated with dark matter halos of mass greater than 10^12 solar masses. We conclude by pointing out the need for infrared space observatories, such as the proposed Next Generation Space Telescope, for pushing the quest for the origin of galaxies beyond z=5.

研究动机与目标

• 通过一种新颖的测光选择技术，识别并表征高红移（z ≈ 3）的原初星系。
• 理解早期星形成星系的物理特性，包括恒星形成速率、星风及尘埃含量。
• 研究高红移星系的团聚特性，并探讨其与冷暗物质模型中暗物质晕形成的关联。
• 评估利用未来红外空间天文台探测z > 5星系的可行性。
• 确定共振散射与星际吸收在塑造早期星系Lyα发射中的作用。

提出的方法

• 采用针对912 Å处莱曼间断的色彩选择技术，以分离高红移星系。
• 利用深度光学与近红外测光，识别具有显著莱曼蓝移特征的星系。
• 通过K波段观测分析紫外连续谱斜率与Hβ发射线，推断尘埃消光。
• 测量蓝移的星际吸收线，以推断星系际介质中的能量星风。
• 应用团聚分析以评估z ≈ 3处的大尺度结构形成。
• 使用冷暗物质（CDM）模型，根据观测到的星团分布推断晕质量。

实验结果

研究问题

• RQ1 z ≈ 3处星系的本质是什么？其物理特性与本地星暴星系相比有何异同？
• RQ2 与其它方法相比，莱曼间断选择技术在探测高红移星系方面有何改进？
• RQ3 尘埃消光在多大程度上影响了早期星系的紫外光度？其定量影响如何？
• RQ4 z ≈ 3星系的团聚尺度是多少？这对其宿主暗物质晕质量有何启示？
• RQ5 探测z > 5星系的前景如何？需要哪些观测设备？

主要发现

• z ≈ 3的星系通常比本地星暴星系亮一个数量级以上。
• 紫外连续谱主要由O型星和早型B型星主导，显著的蓝移星际吸收线表明存在强烈星风。
• Lyα发射较弱，与高中性氢柱密度下的共振散射一致。
• 尘埃消光使紫外光度降低约3倍，该结果由光谱斜率及K波段中Hβ的检测推断得出。
• z ≈ 3处星系的团聚特性表明其宿主暗物质晕质量超过10¹²个太阳质量。
• 观测到的大尺度结构表明，z ≈ 3星系很可能是现今星系团的前身。