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Discovery of a protocluster at z~6

热1 beimu1009 添加于 2012-5-15 13:39 | 3807 次阅读 | 1 个评论

作者
Toshikawa J, Kashikawa N, Ota K, Morokuma T, Shibuya T, Hayashi M, Nagao T, Jiang L, Malkan MA, Egami E, Shimasaku K, Motohara K, Ishizaki Y
摘要
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 6 sigma level, based on the surface number density of i'-dropout galaxies. The overdense region covers ~36 sq. arcmin, and includes 30 i'-dropout galaxies. Follow-up spectroscopy revealed that 15 of these are real z~6 galaxies (5.7 < z < 6.3). Eight of the 15 are clustering in a narrow redshift range 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 Ly-alpha 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 km/s, 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.
详细资料
- 关键词: astro-ph.CO
- 文献种类: Manual Script
- 期卷页: 2012年
- 日期: 2012-3-7
- 发布方式: arXiv e-prints
- 备注:arXiv:1203.1326v1; 12 pages, 9 figures, accepted for publication in ApJ
学科领域自然科学 » 物理学
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