arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2001.00549astro-ph.GAastro-ph.CO
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红移2的成熟星系团的光谱确认

Spectroscopic confirmation of a mature galaxy cluster at redshift two

J. P. Willis, R. E. A. Canning, E. S. Noordeh, S. W. Allen, A. L. King, A. Mantz, R. G. Morris, S. A. Stanford, G. Brammer

摘要:

星系团是宇宙中质量最大的维里化结构,是在宇宙时间内通过物质的引力吸积形成的。一个红移z=2的演化星系团的发现,对应于104亿年的回顾时间,提供了一个研究其性质的机会。星系团XLSSC 122最初在XMM大尺度结构巡天中被发现为一个微弱的扩展X射线源,并被发现与光度红移为1.9 +/- 0.2的致密星系相一致。随后在毫米波长的观测发现,沿着XLSSC 122的视线,Sunyaev-Zel'dovich递减,从而证实了热的星团内气体的存在,而欧洲航天局的X射线多镜任务的深层成像光谱学(XMM-牛顿)揭示了一个扩展的,X射线明亮的气态大气,维里温度为6000万开尔文,富集金属的程度与局部团簇相同。在这里,我们报告的休息框架光学光谱观测XLSSC 122和确定37个成员星系的平均红移为1.98,对应于104亿年的回顾时间。我们使用测光来确定平均无尘恒星年龄为29.8亿年,这表明这些星系中的恒星形成开始于平均红移为12的时候,当时宇宙只有3.7亿年。推断的形成红移的全部范围,包括尘埃的影响,涵盖了从7到13的区间。这些观测结果证实了XLSSC 122是一个非常成熟的星系团,其成员星系中既有演化的恒星星族,又有组成团内介质的炽热富金属气体。

英文摘要:

Galaxy clusters are the most massive virialized structures in the Universe and are formed through the gravitational accretion of matter over cosmic time. The discovery of an evolved galaxy cluster at redshift z=2, corresponding to a look-back time of 10.4 billion years, provides an opportunity to study its properties. The galaxy cluster XLSSC 122 was originally detected as a faint, extended X-ray source in the XMM Large Scale Structure survey and was revealed to be coincident with a compact over-density of galaxies with photometric redshifts of 1.9 +/- 0.2. Subsequent observations at millimetre wavelengths detected a Sunyaev-Zel'dovich decrement along the line of sight to XLSSC 122, thus confirming the existence of hot intracluster gas, while deep imaging spectroscopy from the European Space Agency's X-ray Multi-Mirror Mission (XMM-Newton) revealed an extended, X-ray bright gaseous atmosphere with a virial temperature of 60 million Kelvin, enriched with metals to the same extent as are local clusters. Here we report rest frame optical spectroscopic observations of XLSSC 122 and identify 37 member galaxies at a mean redshift of 1.98, corresponding to a look-back time of 10.4 billion years. We use photometry to determine a mean, dust-free stellar age of 2.98 billion years, indicating that star formation commenced in these galaxies at a mean redshift of 12, when the Universe was only 370 million years old. The full range of inferred formation redshifts, including the effects of dust, covers the interval from 7 to 13. These observations confirm that XLSSC 122 is a remarkably mature galaxy cluster with both evolved stellar populations in the member galaxies and a hot, metal-rich gas composing the intracluster medium.

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