见证星系团在z=1.6处的聚集（z~2 - V处星系的GMASS超深光谱）
Witnessing the assembly at z=1.6 of a galaxy cluster (GMASS ultradeep spectroscopy of galaxies at z~2 - V)
摘要：
我们提出了一个星系overdensity在z=1.6，Cl 0332-2742，发现在银河系质量大会超深光谱巡天（GMASS）的研究。我们保守地估计，在红移空间的尖峰，包含42个星系在z=1.6，为8.3+/-1.5，并找到一个500公里/秒的速度色散。GMASS场中z=1.6的星系表面密度图显示其结构是不规则的。Cl 0332-2742成员星系和场星系物理性质的差异与最新的星系形成模型相一致：过密度成员星系的恒星形成率（SFR）和比SFR比场星系低约50%，过密度星系的平均年龄是场星系的2倍; Cl 0332-2742内的大质量星系（M>10^{10.7} M_sol）和早型星系的比例都比场中的高。在42个成员中，有7个的光谱与被动演化的大质量星系一致。在z-J色星等图中，这些早期型星系的光度数据与理论上红移z=1.6的星系团的红色序列非常一致，该星系团的大部分恒星都是在z~3的恒星形成短爆发中形成的。我们的结论是，在z=1.6的红移尖峰在GMASS领域代表了一个片状结构的宇宙网络和区域内具有最高的表面密度在这个结构，已经包含7个被动演化的星系，将演变成星系团在稍后的时间。
英文摘要：
We present a study of a galaxy overdensity at z=1.6, Cl 0332-2742, uncovered in the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS). We conservatively estimate the overdensity in redshift space for the spike, containing 42 galaxies at z=1.6, to be 8.3+/-1.5 and find a velocity dispersion of 500 km/s. A map of the surface density of galaxies at z=1.6 in the GMASS field shows that its structure is irregular. The differences in the physical properties of Cl 0332-2742 member and field galaxies agree with the latest hierarchical galaxy formation models: for overdensity members, the star formation rate (SFR), and specific SFR, is approximately 50% lower than for the field galaxies; overdensity galaxies are twice the age, on average, of field galaxies; and there is a higher proportion of both massive (M>10^{10.7} M_sol), and early-type galaxies, inside Cl 0332-2742 than in the field. Among the 42 members, 7 have spectra consistent with being passively evolving, massive galaxies. In a z-J colour-magnitude diagram, the photometric data of these early-type galaxies are in close agreement with a theoretical red sequence of a galaxy cluster at redshift z=1.6, which formed most of its stars in a short burst of star formation at z~3. We conclude that the redshift spike at z=1.6 in the GMASS field represents a sheet-like structure in the cosmic web and the area with the highest surface density within this structure, containing already seven passively evolving galaxies, will evolve into a cluster of galaxies at a later time.
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