DISCOVERY OF A PROTOCLUSTER AT z ∼ 6
DISCOVERY OF A PROTOCLUSTER AT z ∼ 6
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DOI：
10.1088/0004-637x/750/2/137
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发表时间：
2012-03
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通讯作者：
J. Toshikawa;N. Kashikawa;K. Ota;T. Morokuma;T. Shibuya;M. Hayashi;T. Nagao;Linhua Jiang;M. Malkan;E. Egami;K. Shimasaku;K. Motohara;Yoshifumi Ishizaki
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文献类型：
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作者：
J. Toshikawa;N. Kashikawa;K. Ota;T. Morokuma;T. Shibuya;M. Hayashi;T. Nagao;Linhua Jiang;M. Malkan;E. Egami;K. Shimasaku;K. Motohara;Yoshifumi Ishizaki
我们报告发现的原星系团在z 106包含至少8个集群成员星系的光谱确认在宽视场图像的斯巴鲁深场（SDF）。根据i′-dropout星系的表面数密度，在6σ水平上原星系团的过密度是显著的。过密区的面积为14 Mpc × 14 Mpc（z = 6时的共动单位），包括30个i′-dropout星系。后续的光谱分析显示，其中15个是真实的z <6的星系（5.7 < z < 6.3）。在这15个星系中，有8个星系聚集在一个狭窄的红移范围内（Δz < 0.05，以z = 6.01为中心），对应于红移空间平均数密度的7倍增加。我们发现，在所观测到的性质，如Lyα光度和紫外连续谱的幅度，8个原星系团成员和7个非成员之间没有显着差异。八个原星团成员的速度色散为647 ± 124 km s−1，比标准冷暗物质模型预测的高出约三倍。这种差异可以归因于8个原星团成员的独特三维分布。我们讨论了这种差异的两种可能的解释：要么原星系团已经成熟，在中心的老星系，或者它仍然是不成熟的，由三个分组合并成为一个更大的集群。无论是哪种情况，SDF中z = 6.01的星系可能是宇宙中星系团形成的第一个地点之一。
We report the discovery of a protocluster at z ∼ 6 containing at least eight cluster member galaxies with spectroscopic confirmations in the wide-field image of the Subaru Deep Field (SDF). The overdensity of the protocluster is significant at the 6σ level, based on the surface number density of i′-dropout galaxies. The overdense region covers ∼6′ × 6′ (14 Mpc × 14 Mpc in comoving units at z = 6) and includes 30 i′-dropout galaxies. Follow-up spectroscopy revealed that 15 of these are real z ∼ 6 galaxies (5.7 < z < 6.3). Of these 15, 8 are clustering in a narrow redshift range (Δz < 0.05 centered at z = 6.01), corresponding to a seven-fold increase in number density over the average in redshift space. We found no significant difference in the observed properties, such as Lyα luminosities and UV continuum magnitudes, between the eight protocluster members and the seven non-members. The velocity dispersion of the eight protocluster members is 647 ± 124 km s−1, which is about three times higher than that predicted by the standard cold dark matter model. This discrepancy could be attributed to the distinguishing three-dimensional distribution of the eight protocluster members. We discuss two possible explanations for this discrepancy: either the protocluster is already mature, with old galaxies at the center, or it is still immature and composed of three subgroups merging to become a larger cluster. In either case, this concentration of z = 6.01 galaxies in the SDF may be one of the first sites of formation of a galaxy cluster in the universe.