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arXiv 0909.3160astro-ph.CO
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z=1.2时大尺度结构中星系的成星活动

Star Formation Activities of Galaxies in the Large-Scale Structures at z=1.2

M. Tanaka, C. Lidman, R. G. Bower, R. Demarco, A. Finoguenov, T. Kodama, F. Nakata, P. Rosati

备注：
12 pages, 12 figures. Accepted for publication in A&A
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摘要：

最近对z=1.24的X射线发光星系团RDCSJ 1252.9 -2927进行的宽视场成像观测发现了几个星系群，它们似乎嵌入在从星系团核心延伸出来的平行结构中。我们使用双子座南的GMOS和VLT上的FORS 2对这些星系群中的星系进行了光谱研究，目的是确定这些星系是否与星系团有物理联系。我们发现，三组包含星系团红移，他们可能是绑定到集群。这是第一次确认星系群在z>1时所追踪到的星系结构。然后，我们使用FORS 2光谱中的几个光谱特征来确定星系群的恒星形成历史。我们在星系团核心的星系群中发现了一群相对红色的恒星形成星系。虽然类似的红色恒星形成星系也可以在现场发现，hd线的平均强度是系统性较弱的星系群。有趣的是，这些z=1.2的群体所处的环境中，红色序列正在不断积累。这种不寻常的谱线强度可以用被尘埃严重遮蔽的恒星形成来解释。我们假设，星系-星系的相互作用，这是更有效的组环境，是驱动这些尘埃遮蔽恒星形成的机制。该假设可以通过获得近红外光谱观测、高分辨率成像观测和中红外观测来检验。

英文摘要：

Recent wide-field imaging observations of the X-ray luminous cluster RDCSJ1252.9-2927 at z=1.24 uncovered several galaxy groups that appear to be embedded in filamentary structure extending from the cluster core. We make a spectroscopic study of the galaxies in these groups using GMOS on Gemini-South and FORS2 on VLT with the aim of determining if these galaxies are physically associated to the cluster. We find that three groups contain galaxies at the cluster redshift and that they are probably bound to the cluster. This is the first confirmation of filamentary structure as traced by galaxy groups at z>1. We then use several spectral features in the FORS2 spectra to determine the star formation histories of group galaxies. We find a population of relatively red star-forming galaxies in the groups that are absent from the cluster core. While similarly red star forming galaxies can also be found in the field, the average strength of the hd line is systematically weaker in group galaxies. Interestingly, these groups at z=1.2 are in an environment in which the on-going build-up of red sequence is happening. The unusual line strengths can be explained by star formation that is heavily obscured by dust. We hypothesize that galaxy-galaxy interactions, which is more efficient in the group environment, is the mechanism that drives these dust obscured star formation. The hypothesis can be tested by obtaining spectral observations in the near-IR, high resolution imaging observations and observations in the mid-IR.

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